[build] Allow building PCI ROMs with device ID lists

PCI v3.0 supports a "device list" which allows the ROM to claim
support for multiple PCI device IDs (but only a single vendor ID).
Add support for building such ROMs by scanning the build target
element list and incorporating any device IDs into the ROM's device
list header.  For example:

  make bin/8086153a--8086153b.mrom

would build a ROM claiming support for both 8086:153a and 8086:153b.

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

src/arch/i386/scripts/i386.lds

@@ -41,6 +41,7 @@ SECTIONS {
     .prefix 0x0 : AT ( _prefix_lma ) {
 	_prefix = .;
 	*(.prefix)
+	*(SORT(.pci_devlist.*))
 	*(.prefix.*)
 	_mprefix = .;
     } .bss.prefix (NOLOAD) : AT ( _end_lma ) {