boot-directdisk: Allow for EFI-only boot direct disk images
Condition building PCBIOS legacy images on MACHINE_FEATURES containing "pcbios"
or not containing "efi". This ensures existing BSPs will continue to get the
old PCBIOS legacy-only images. New BSPs can add "efi", "pcbios", or both. The
images created likewise support one or the other or both.
Signed-off-by: João Henrique Ferreira de Freitas <joaohf@gmail.com> Signed-off-by: Saul Wold <sgw@linux.intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
