msm: kgsl: Dump registers through debug AHB path on A6XX

Some registers are accessible through the debug AHB path instead
of the usual AHB path. Add these registers to the A6XX snapshot.

Change-Id: Iad6413ab18792d9953840dadd200b54db8eda824
Signed-off-by: Lynus Vaz <lvaz@codeaurora.org>