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: Id9fa12a3521462ddef34eb1a0a91f14c2f558a67
Signed-off-by: Amit Nischal <anischal@codeaurora.org>