msm: kgsl: Reset VSC control registers

Configure the A2xx VSC register in context switch,
which helps GPU to recover from the bad state.

CRs-Fixed: 637288
Change-Id: I2000a579614c491a015c618a52808500541329c5
Signed-off-by: Hareesh Gundu <hareeshg@codeaurora.org>
msm: kgsl: Fix for panic in z180 postmortem dumps

We were accessing z180 registers without holding
device mutex. This change ensures that we hold the
mutex before accessing z180's registers

CRs-Fixed: 644283
Change-Id: Ib6496c427fc6c9a3f97a6720adb80a390fe21b0d
Signed-off-by: Gaurav Gagrani <ggagrani@codeaurora.org>
Signed-off-by: Hareesh Gundu <hareeshg@codeaurora.org>