ARM: dts: msm: add device phy ref_clk pad rail for MSM8994

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 rail on MSM8994.

Change-Id: Idba39523c8ccb713fc2cfec8ab2d6381b5f4b644
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>