ARM: dts: msm: Enable qcom,power-always-on for GPU SMMUs on GKI targets

When unmapping memory, the SMMU driver must access the GPU SMMU's
register space, so it must vote for power resources to access the TLB
invalidation registers. When the GPU is in slumber, there aren't votes
for the GPU SMMU's power resources, so the SMMU driver constantly ends
up enabling/disabling the power resources, which takes a considerable
amount of time. When paired with the suboptimal IOMMU page table
management code, this leads to performance issues where the time taken
to unmap memory is large.

Thus, for all targets that support GKI, add the qcom,power-always-on
property for the GPU SMMUs of these targets, to remove the latency
incurred by having to enable/disable power resources in the GKI
configuration.

Change-Id: I403c9864705c50f7ce8b1118c3c75902708e647b