feat(ff-a): support FFA_MSG_SEND_DIRECT_REQ2/RESP2

StandaloneMm which is S-EL0 partition uses
FFA_MSG_SEND_DIRECT_REQ2/RESP2 to handle multiple services.
For this, add support for FFA_MSG_SEND_DIRECT_REQ2/RESP2 in el3_spmc
restrictly up to use 8 registers.
although FF-A v1.2 defines FFA_MSG_SEND_DIRECT_REQ2/RESP2
with ability to pass/return up to 18 registers.

Signed-off-by: Levi Yun <yeoreum.yun@arm.com>
Change-Id: I8ab1c332d269d9d131330bb2debd10d75bdba1ee
4 files changed