msm: kgsl: Don't use GMU for bandwidth voting on legacy targets

Legacy target's GMU firmware doesn't support bandwidth voting.
Add a check to make sure GMU is used for bandwidth voting only
on those targets where GMU firmware supports it.

Change-Id: I96ffdafe489bcb85caefbaa1fe980838fdce9cf2
Signed-off-by: Deepak Kumar <dkumar@codeaurora.org>