msm: pil-modem: Migrate to clk APIs for XO voting

Use the clock APIs instead of the msm_xo APIs to vote on PXO.
This removes one more msm specific api from this driver and will
allow us to move XO control into the rpm clock driver.

Change-Id: Ie7d862131a7b8717c3ab0574f570f073c6a69dfd
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>