USB: phy-msm-usb: Remove old XO voting implementation

Now drivers need to explicitly enable or disable xo_clk
for voting for XO ON or OFF. Hence the old XO voting
APIs are not needed anymore. Also msm_xo header file
is not moved to common location.
Hence remove the old XO voting mechanism.

Change-Id: I8e313727aa44faf895ebbacf46538dcd28788572
Signed-off-by: Sujeet Kumar <ksujeet@codeaurora.org>