msm: kgsl: Need to explicitly halt the ME on stop

it seems even if gpu requests for power rail off, modem might not
process this request as it leads to turn off power rail for mdp in
the case of 7x27a/8x25. This issue specific to 7x27a, since we do
soft reset the GPU on sleep/wake. In the case of suspend/resume,
the powerail is effectively off across the device.

Change-Id: Iad898da67b34e265b2447013c4250ba04a59c0cd
Signed-off-by: Rammohan Basavaraju <rammoh@codeaurora.org>