feat(ff-a): define memory security state attribute

FF-A v1.1rel0 defines the security state attribute for the
memory transaction descriptor. Add respective definition
to ffa_helpers.h.

Signed-off-by: J-Alves <joao.alves@arm.com>
Change-Id: Iefb510f5272587bc9faa96731af0159e2379576b
1 file changed