clk: qcom: gpucc-sm8150: mark gpu_cc_ahb_clk as critical

Add the CLK_IS_CRITICAL flag for gpu_cc_ahb_clk to keep it
enabled at all times.  This is needed to avoid unclocked
register accesses by SMMU since SMMU vote registers do not
enable gpu_cc_ahb_clk.

Also skip an enable check for this clock since it will not
be physically enabled until gpu_cx_gdsc is enabled.

Change-Id: I826fc168a4a5a82aae99b9e51dc0230e8b8cb0fc
Signed-off-by: David Collins <collinsd@codeaurora.org>