msm: kgsl: Remove KGSL_PROP_GPMU_VERSION property

This property appears to be unused. Removing this lets us make the
GPMU / GMU versions platform specific which should serve us better
than having it in the generic list.

Change-Id: Ic0dedbadcac211680a5a18a9ec1de8b618233a04
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>