msm: kgsl: Add support for gtcu-ahb-clk

For graphics self-programming in MSM8916, the KGSL driver needs to
enable the gtcu-ahb-clk. Need to turn on this clock only when GPU
programs ARM SMMU. CPU takes a different route to program the same
SMMU. Hence when using global page tables, this clock need not be
enabled.

Change-Id: Ibc774abe8b89986eae89c435032656c7ce65e769
Signed-off-by: Lokesh Batra <lbatra@codeaurora.org>