msm: kgsl: Consolidate gmu register programming

Make a single function to configure gmu registers before
gmu boot. This will be used by hardware dispatcher as well.
Also, get rid of gmu->load_mode since it's always been
TCM BOOT.

Change-Id: I832b450e25cb1e76f0294a053eb9880759e65229
Signed-off-by: Harshdeep Dhatt <hdhatt@codeaurora.org>