msm: kgsl: Make use of the new clock APIs.

Use the split clock APIs to do low latency actions (enable/disable)
frequently.  Use the high latency functions (prepare/unprepare)
sparingly to help performance.

CRs-fixed: 351696
Change-Id: Iaf9ed2117a1647e38be8658c60a365d377c968a4
Signed-off-by: Lucille Sylvester <lsylvest@codeaurora.org>