msm: kgsl: Use one entry point for external HFI requests

For HFI requests that do not originate from HFI itself,
use a generic HFI function as the entry point. This keeps
the usage of different HFI requests simple and easy to
maintain when other functions start relying on HFI requests
more regularly.

Change-Id: I15213ebd6fa3e04a71c0727cf46920f6a2414af3
Signed-off-by: Carter Cooper <ccooper@codeaurora.org>