iommu/arm-smmu: Add support for not removing SMMU power votes

The SMMU driver will vote for the resources it needs before performing
a particular operation, and will remove its votes after the operation
is complete.

When power resources are not currently enabled by other drivers,
the SMMU driver's requests to enable its devices' power resources
go through the slow paths where the hardware power resources
get turned on. So, in a scenario where the SMMU driver is constantly
performing work and having to toggle the state of the power resources,
the SMMU driver operations take more time.

On GKI, the upstream implementation of the IOMMU page table management
code is used, which doesn't have the optimizations we have downstream,
which improve the performance of the SMMU driver when unmapping memory.

The GPU can go into slumber if it is not active, and can relinquish its
votes for the power resources that the SMMU driver votes for when
unmapping memory. This requires the SMMU driver to take the slowpath
of enabling all of these power resources and then disabling them
on every call to unmap memory, which can incur a considerable amount
of delay.

This delay, along with the usage of the unoptimized IOMMU page table
management code in GKI results in slow unmap calls.

Thus, add support for the SMMU driver to never remove its power votes,
so that it doesn't have to spend time voting for power resources while
it is operating.

Change-Id: Id93aafef18f69e377391875e2a7b340b34b4b3e8
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>