Out of two possible implementation of Secure Partition Manager(SPM)
currently only Management mode (MM) design is supported and the support
for SPM based on SPCI Alpha 1 prototype has been removed.

Earlier both implementation used common build flag "ENABLE_SPM" but it
has since been decoupled and MM uses a separate build FLAG "SPM_MM".

Instructions to build it for FVP was still using "ENABLE_SPM", which has
beend corrected in this patch.

Signed-off-by: Manish Pandey <manish.pandey2@arm.com>
Change-Id: I505b98173d6051816436aa602ced6dbec4efc776