msm: kgsl: Synchronize access to IOMMU cfg port

Add a software based spinlock between CPU and GPU.
This spinlock is used to grant mutually exclusive access to
SMMU configuration between CPU and GPU. This mutual exclusion
is required to prevent deadlock in the system.

CRs-Fixed: 409198
Change-Id: Ic375beaaf4c5505b41d3fabc4adf15965d71b13a
Signed-off-by: Tarun Karra <tkarra@codeaurora.org>
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: Rajeev Kulkarnie <krajeev@codeaurora.org>