x86/vga: set the default device from the fixup.

Since Matthew's efi/vga changes on non-EFI machines we were failing
to tell the vgaarb/switcheroo what the default device was, this
sets the default device in the quirk if none has been set before.

This fixes the switcheroo on my T410s.

Cc: Matthew Garrett <mjg@redhat.com>
Acked-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>