docs(spm): document s-el0 partition support

This patch adds a brief description of S-EL0 partition support in the
SPMC using ARMv8.1 FEAT_VHE.

Signed-off-by: Raghu Krishnamurthy <raghu.ncstate@gmail.com>
Change-Id: Ie079265476604f62d5f2a66684f01341000969d0
1 file changed