[settings] Expose PCI configuration space via settings mechanism

Allow values to be read from PCI configuration space using the syntax

  ${pci/<busdevfn>.<offset>.<length>}

where <busdevfn> is the bus:dev.fn address of the PCI device
(expressed as a single integer, as returned by ${net0/busloc}),
<offset> is the offset within PCI configuration space, and <length> is
the length within PCI configuration space.

Values are returned in reverse byte order, since PCI configuration
space is little-endian by definition.

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

src/config/config.c

@@ -298,6 +298,9 @@ REQUIRE_OBJECT ( efi_bofm );
 /*
  * Drag in relevant settings sources
  */
+#ifdef PCI_SETTINGS
+REQUIRE_OBJECT ( pci_settings );
+#endif
 #ifdef VMWARE_SETTINGS
 REQUIRE_OBJECT ( guestinfo );
 #endif

src/config/settings.h

@@ -9,6 +9,7 @@
 
 FILE_LICENCE ( GPL2_OR_LATER );
 
+#define	PCI_SETTINGS	/* PCI device settings */
 //#define	VMWARE_SETTINGS	/* VMware GuestInfo settings */
 
 #include <config/local/settings.h>