feat(spmd): el3 direct message API

This patch implements an API that is exposed to SPMD logical partitions
that can be used to send direct messages to a secure partition.
It also adds required code in the SPMD smc handler to complete the
direct response appropriately.

Change-Id: I2d0e38415f13ad4fd28f8984d565036b7d3a9e71
Signed-off-by: Raghu Krishnamurthy <raghu.ncstate@gmail.com>
4 files changed