msm: kgsl: Move HFI to the a6xx space

The next step in the GMU transition is to move HFI to a6xx target specific
code. Rename the file, functions and kgsl_hfi struct.

Change-Id: Ic0dedbad7efcda12f03fbd37bb2267296ee7a5ac
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>