msm: kgsl: Disable coresight before snapshot if already enabled

Concurrently running coresight while dumping debug bus registers
breaks coresight. In these instances, disable coresight first,
collect snapshot and then re-enable coresight.

However, since this disabling is temporary, do not disable
through coresight_disable() call, instead disable coresight
by programming GPU coresight registers.

CRs-fixed: 656398
Change-Id: Icc3ddfe88c17777e3132a1e03994b263d0d241a4
Signed-off-by: Harsh Vardhan Dwivedi <hdwivedi@codeaurora.org>