scsi: ufs-qcom: add support to control the device ref_clk

On Qualcomm platforms, there will be many consumers of the source clock
which also supply ref_clk to UFS Device. So even if generic UFS
driver (ufshcd) vote to turn off the source ref_clk, it's very likely that
device ref_clk is still running. Hence some of the qualcomm chipsets have
separate control bit to gate & ungate the UFS ref_clk to device. This
control bit is part of the TLMM register adddress space so it can't be
simulated at clock control bit which means UFS qcom driver has to manually
control this bit to gate or ungate the device ref_clk. This change adds
support for the same.

Change-Id: I3ee1187292eaadfdb552d33c2bb6f58922c9e501
[subhashj@codeaurora.org: resolved merge conflicts, dropped changes to
msm8994.dtsi]
Signed-off-by: Subhash Jadavani <subhashj@codeaurora.org>
[venkatg@codeaurora.org: resolved trivial merge conflicts,
drop changes to include/linux/phy/phy-qcom-ufs.h]
Signed-off-by: Venkat Gopalakrishnan <venkatg@codeaurora.org>