fix(smccc): check smc_fid [23:17] bits

fix(smccc): check smc_fid [23:17] bits

As per SMCCC spec Table 2.1 bit 23:17 must be zero (MBZ),
for all Fast Calls, when bit[31] == 1.
Adding this check to ensure SMC FIDs when get to the SMC handler
have these bits (23:17) cleared, if not capture and report them
as an unknown SMCs at the core.

Also the C runtime stack is copied to the stackpointer well in
advance, to leverage the existing el3_exit routine for unknown SMC.

Change-Id: I9972216db5ac164815011177945fb34dadc871b0
Signed-off-by: Jayanth Dodderi Chidanand <jayanthdodderi.chidanand@arm.com>