perf(spmd): omit sel1 context save if sel2 present
perf(spmd): omit sel1 context save if sel2 present

The SPMC at S-EL2 manages S-EL1 execution contexts for SPs. The
currently running SP vCPU state is always saved when the SPMC exits to
SPMD. A fresh vCPU context is always restored when the SPMC is entered
from the SPMD and a SP resumed. For performance optimization reasons
this permits omitting the saving/restoring of the S-EL1 context from
within the EL3 SPMD on entering/exiting the SPMC. The S-EL2 SPMC and
NS-EL1 context save/restore remain done in the SPMD.

Signed-off-by: Olivier Deprez <a71d93c73db536dc855a04902dabc350f140693d@arm.com>
Change-Id: I66413ed5983913791ff5c9fc03c590ee65c6ccd7

achingupta/arm-trusted-firmware,achingupta/arm-trusted-firmware