msm: kgsl: Do not access GMU_HFI_ON flag in power control

HFI is not a common feature, it's specific to few A6xx GPUs.
Move HFI flags related operations inside GMU module.

Change-Id: I3041533854389514c6737b167dd5c4b521886924
Signed-off-by: Hareesh Gundu <hareeshg@codeaurora.org>