scsi: ufs: skip devoting device ref_clk during clock gating

Voting/devoting device ref_clk source could be time consuming hence add
support to allow ufs variant to decide if it wants to control ref_clk
during aggressive clock gating or not. This clock should still be gated
off during runtime/system suspend.

Change-Id: Ibec8cc8b3689ff4e2418039e74dbf311e589157e
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>