phy: qcom-ufs: add optional ref aux clk

Newer platforms need an additional ref aux clk to be enabled, add support
for the new ref aux clk and make it optional as its not needed by other phy
versions.

Change-Id: I5e04980eb451b193e9c024bfe35383d10d17feff
Signed-off-by: Venkat Gopalakrishnan <venkatg@codeaurora.org>
[cang@codeaurora.org: resolved trivial merge conflicts]
Signed-off-by: Can Guo <cang@codeaurora.org>