clk: qcom: clk-alpha-pll: add callbacks to deal with voltage voting

Specify prepare, unprepare, pre_change_rate, post_change_rate callbacks
for alpha-pll clk_ops.  This ensures that supply regulator requirements
are managed properly at runtime.

Change-Id: I578b81c2ab77a8d7e2332098bd737b0646cf577d
Signed-off-by: David Dai <daidavid1@codeaurora.org>