refactor(arm): avoid setting HASH_PREREQUISITES for a build without ROT_KEY

In the absence of ROT_KEY option, there is no need to populate
HASH_PREREQUISITES as the build system uses the hash file specified by
ARM_ROTPK_HASH directly.

Change-Id: Ib08f53b182b8446bbc430f2608471c7dfdc0e58c
Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
1 file changed