clk: qcom: Add GPU clock driver for SM6150

Add support for the graphics clock controller found on SM6150
based devices. This should allow GPU device drivers to probe
and control their clocks.

Change-Id: Ic4dc10771a4ea79d181be38e6f1594ecc6f314d3
Signed-off-by: Veera Vegivada <vvegivad@codeaurora.org>