SPM: EHF: Build EHF module along with Secure Partition Manager

Add a dependency for building EL3 exception handling framework(EHF)
module with the secure partition manager(SPM).

The EHF module is needed for raising the core's running priority
before the core enters the secure partition, and lowering it
subsequently on exit from the secure partition.

Change-Id: Icbe2d0a63f00b46dc593ff3d86b676c9333506c3
Signed-off-by: Sughosh Ganu <sughosh.ganu@arm.com>