msm: kgsl: Dump GPU_UCHE_GBIF_GX_CONFIG register in snapshot

GPU_UCHE_GBIF_GX_CONFIG is programmed as a part of software
workaround for HW errata#171. Dump it in snapshot to allow
SDA report to identify whether software workaround is present
or not.

Signed-off-by: Deepak Kumar <dkumar@codeaurora.org>
Change-Id: Ic971f4f660d03529ddb265663f8a44b5c2f22a34