msm: kgsl: Use hard coded GMU frequency and CX voltage levels

We only need to specify the CX voltage levels that are needed by GMU.
Hence we do not need to hardcode all the CX voltage levels. This way,
we do not need an OPP table created and queried for this information.

Change-Id: I700fd455020e8ebf653810cec1bce4f53599ff73
Signed-off-by: Raghu Ananya Arabolu <rarabolu@codeaurora.org>