iommu/arm-smmu: Make atomic scm call in slave side protection mode

When we have SMMU halt/resume functionality
enabled we try to program MICRO_MMU_CTRL register
which is part of SMMU implementation defined
register space. Now targets which have slave side
protection mechanism, implementation defined
register space of SMMU is protected by XPUs along
with other SMMU global register space. As a result
we would get a fault if we directly try to program
MICRO_MMU_CTRL register.

Instead we request TZ through atomic scm call to
program this register for us. Since we have read only
permission available for these registers we need to
ensure that write operation is requested through TZ.

CRs-Fixed: 959535
Change-Id: Ie257553a25bb11785b69568d8eccbef91d8d18e0
Signed-off-by: Susheel Khiani <skhiani@codeaurora.org>