ANDROID: KVM: arm64: iommu: Harden __pkvm_iommu_pm_notify

Currently __pkvm_iommu_pm_notify always changes the value of
dev->powered following a suspend/resume attempt. This could potentially
be abused to force the hypervisor to stop issuing updates to an S2MPU
and preserving an old/invalid state.

Modify to only update the power state if suspend/resume was successful.

Bug: 190463801
Signed-off-by: David Brazdil <dbrazdil@google.com>
Change-Id: I285fc822e9fc926c49b9b5e69446790e1edccafb