msm: kgsl: Always boot GMU with default CM3 config

Ensure that CM3 configuration is always set to default value
before taking CM3 out of reset. Also make sure that we
read/modify this register when we send NMI to GMU.

Change-Id: Ic9c4506c04c5e7dd1cabf12901fa53636e2ed9c7
Signed-off-by: Oleg Perelet <operelet@codeaurora.org>