xcompile: specify arm64 subarches

This tells abuild that it can in fact build arm64
images.

Change-Id: I47695372053513ca039e118776aa904ea0afa21d
Signed-off-by: Patrick Georgi <pgeorgi@google.com>
Reviewed-on: http://review.coreboot.org/8474
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@google.com>
1 file changed