efifb: Implement vga_default_device() (v2)

EFI doesn't typically make use of the legacy VGA ROM, but it may still be
configured to pass that through to a given video device. This may lead to
an inaccurate choice of default video device. Add support to efifb to pick
out the correct active video device.

v2: fix if->ifdef

Signed-off-by: Matthew Garrett <mjg@redhat.com>
Acked-by: hpa@zytor.com
Cc: matt.fleming@intel.com
Signed-off-by: Dave Airlie <airlied@redhat.com>

arch/x86/include/asm/vga.h

@@ -17,4 +17,10 @@
 #define vga_readb(x) (*(x))
 #define vga_writeb(x, y) (*(y) = (x))
 
+#ifdef CONFIG_FB_EFI
+#define __ARCH_HAS_VGA_DEFAULT_DEVICE
+extern struct pci_dev *vga_default_device(void);
+extern void vga_set_default_device(struct pci_dev *pdev);
+#endif
+
 #endif /* _ASM_X86_VGA_H */