iommu: arm-smmu: Save and restore s1 bypass state for cb

Save the S1 bypass state for context bank and restore it during
hibernation restore. Current implementation of 'cb write' function
has a bug, in which if it's called with attributes = 0; it blindly
sets SCTLR_M bit which ignores the S1 bypass. This patch fixes
this bug.

Change-Id: Ib108cc4ffa315091cd4954a574dde6beb4dac9b3
Signed-off-by: Omkar Savagaonkar <omkars@codeaurora.org>