device/oprom/realmode: Sanitize header inclusion

Alphabetise includes to avoid duplication.

Change-Id: I7fa6998cd736bad2bab4a6b1a65d48a21d6220d9
Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Reviewed-on: http://review.coreboot.org/6415
Tested-by: build bot (Jenkins)
Reviewed-by: Isaac Christensen <isaac.christensen@se-eng.com>