msm: kgsl: Clear pending transactions from VBIF on hang

When resetting device on a hang the pending transactions in the
VBIF should be cleared since the GPU is hung and unable to accept
any transactions. These pending transactions can cause VBIF pipe
to block the IOMMU so clear them.

CRs-Fixed: 762073
Change-Id: I05b2f5ab5af0e517835dd79a9630c1ee4750020f
Signed-off-by: Shubhraprakash Das <sadas@codeaurora.org>
Signed-off-by: Hareesh Gundu <hareeshg@codeaurora.org>