[build] Include USB drivers in the all-drivers build by default

Including USB drivers has some unavoidable side effects.  With a BIOS
firmware, attaching the host controller drivers will necessarily
disable the SMM-based USB legacy support which emulates a PS/2
keyboard.  With a UEFI firmware, loading the host controller drivers
may disconnect some of the less compliant vendor USB device drivers.

We have historically erred on the side of caution and avoided
including any USB drivers in the all-drivers build.  Time has moved
on, USB NICs have become more common (especially for laptops, which
now rarely include physical Ethernet ports), and the UEFI Secure Boot
model makes it prohibitively difficult for users to compile their own
binaries to add support for non-default drivers.

Switch to including USB drivers by default in the all-drivers build.
Provide a fallback build target that matches the existing driver set
(i.e. excluding any USB drivers) and can be built using e.g.:

   make bin/ipxe-legacy.iso

   make bin-x86_64-efi/ipxe-legacy.efi

Signed-off-by: Michael Brown <mcb30@ipxe.org>

.github/workflows/build.yml

@@ -38,6 +38,8 @@ jobs:
                ${{ env.bindir }}/ipxe.lkrn \
                ${{ env.bindir }}/ipxe.pxe \
                ${{ env.bindir }}/ipxe.usb \
+               ${{ env.bindir }}/ipxe-legacy.lkrn \
+               ${{ env.bindir }}/ipxe-legacy.pxe \
                ${{ env.bindir }}/undionly.kpxe \
                ${{ env.bindir }}/errors
 
@@ -57,6 +59,8 @@ jobs:
           path: |
             src/${{ env.bindir }}/ipxe.lkrn
             src/${{ env.bindir }}/ipxe.pxe
+            src/${{ env.bindir }}/ipxe-legacy.lkrn
+            src/${{ env.bindir }}/ipxe-legacy.pxe
             src/${{ env.bindir }}/undionly.kpxe
             src/${{ env.bindir }}/errors
             src/${{ env.bindir }}/niclist.txt
@@ -126,6 +130,7 @@ jobs:
           make ${{ env.bindir }}/ipxe.efi \
                ${{ env.bindir }}/ipxe.iso \
                ${{ env.bindir }}/ipxe.usb \
+               ${{ env.bindir }}/ipxe-legacy.efi \
                ${{ env.bindir }}/snponly.efi \
                ${{ env.bindir }}/errors
 
@@ -136,6 +141,7 @@ jobs:
           if-no-files-found: error
           path: |
             src/${{ env.bindir }}/ipxe.efi
+            src/${{ env.bindir }}/ipxe-legacy.efi
             src/${{ env.bindir }}/snponly.efi
             src/${{ env.bindir }}/errors
 
@@ -234,14 +240,14 @@ jobs:
       image: ghcr.io/ipxe/ipxe-signer
     env:
       binaries: >-
-        bin-x86_64-pcbios/ipxe.lkrn
-        bin-arm32-efi/ipxe.efi
-        bin-arm64-efi/ipxe.efi
-        bin-i386-efi/ipxe.efi
-        bin-loong64-efi/ipxe.efi
-        bin-riscv32-efi/ipxe.efi
-        bin-riscv64-efi/ipxe.efi
-        bin-x86_64-efi/ipxe.efi
+        bin-x86_64-pcbios/${DRIVERS}.lkrn
+        bin-arm32-efi/${DRIVERS}.efi
+        bin-arm64-efi/${DRIVERS}.efi
+        bin-i386-efi/${DRIVERS}.efi
+        bin-loong64-efi/${DRIVERS}.efi
+        bin-riscv32-efi/${DRIVERS}.efi
+        bin-riscv64-efi/${DRIVERS}.efi
+        bin-x86_64-efi/${DRIVERS}.efi
     steps:
 
       - name: Check out code
@@ -262,8 +268,11 @@ jobs:
               Press Ctrl-B for the iPXE command line... \
               && shell || autoboot
           EOF
-          ./src/util/genfsimg -o ipxe.iso ${{ env.binaries }}
-          ./src/util/genfsimg -o ipxe.usb -s autoexec.ipxe ${{ env.binaries }}
+          for DRIVERS in ipxe ipxe-legacy ; do
+              ./src/util/genfsimg -o ${DRIVERS}.iso ${{ env.binaries }}
+              ./src/util/genfsimg -o ${DRIVERS}.usb -s autoexec.ipxe \
+                                  ${{ env.binaries }}
+          done
 
       - name: Upload
         uses: actions/upload-artifact@v6
@@ -273,6 +282,8 @@ jobs:
           path: |
             ipxe.iso
             ipxe.usb
+            ipxe-legacy.iso
+            ipxe-legacy.usb
 
   publish:
     name: Publish