scsi: ufs-qcom: add device ref_clk pad regulator voting support

UFS device's phy ref_clk is sourced via MSM's ref_clk pad. This pad is
having its own power domain which is powered by 1.2v rail. This change
adds the voting support for this pad rail.

Change-Id: I179b2b9bb7ef2e7938ba0aaa87faed09cdad6139
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>