ANDROID: KVM: arm64: Don't update IOMMUs for share/unshare

Share/unshare initiated by host doesn't change memory permission, and
as currently pKVM doesn't support device assignment, there is no need
to update the IOMMU unnecessarily as it waste cycles.

Once device assignment is enabled, this assumption will not be valid
as guests have access to DMA.

Bug: 291843613
Change-Id: I28c69ec8f721711d5b59fa2784386fa61654fe5a
Signed-off-by: Mostafa Saleh <smostafa@google.com>