iommu: smmu: Power on smmu during ATOS operation

In case of MMU-500, the smmu hardware maybe integrated in a
way that both TCU and TBUs are tied up to a single GDSC and
clocks block, where putting the required votes for TCU would
power ON the TBUs as well and no such votes for TBUs are
required or available. Currently, the arm-smmu driver powers
ON only the TBU during ATOS operation, which has no effect in
such hardware configuration. Hence, power ON the TCU.

Change-Id: I940b1696d1a60997276337854ee98993d88a9cd8
Signed-off-by: Sudarshan Rajagopalan <sudaraja@codeaurora.org>