msm: kgsl: Remove gmu_core_dev_enable_lm function

This function writes to GMU CX/AO registers which can be
configured much earlier in gmu code itself instead.

Change-Id: I403ad8d2e0fa4f199663f0fb6234de3e59bd05f9
Signed-off-by: Harshdeep Dhatt <hdhatt@codeaurora.org>