usb: msm_otg: vote and unvote for TCXO through XO API

USB PHY takes TCXO clock as input and using the PHY internal PLL,
gets the 480MHz clock for USB operations. While USB PHY is suspended,
the TCXO clock can be turned off.
On 8960 target, mandating that TCXO clock users must need to vote for
TCXO and if all the users vote for TCXO clock-off, then MSM can switch to
lower power clock and can run.

Change-Id: Ia9a91bca52a1003439a3a38bbd8eb835dbf349e1
Signed-off-by: Anji jonnala <anjir@codeaurora.org>
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>