clk: msm: msm8937: Enable using sleep_vote for gpll0

Introduce a new clock as gpll0_sleep_clk_src as parent of gpll0_clk_src
which is used by all non-cpu clients in HLOS. This sleep clock will clear
the sleep bit for gpll0 when enabled and set the sleep bit when disabled.
Thus it is ensured that GPLL0 sleep-vote is set only when there is no
client in HLOS using it.

Change-Id: Ifab19eb6455269eb6b19223c1ae402701cbe1e91
Signed-off-by: Jaydeep Sen <jsen@codeaurora.org>