msm: clock: Move voltage scaling to prepare/unprepare

Move the voltage calls to a sleepable context so we can avoid
spinning for hundreds of microseconds with interrupts disabled
waiting for a regulator to increase. This change also paves the
way to making the clock driver into a real regulator consumer
that uses the proper regulator APIs instead of the MSM specific
rpm_vreg API.

Doing this also requires us to make clk_set_rate() a sleeping
call so that concurrent clk_prepare() and clk_set_rate() calls
are synchronized. Making clk_set_rate() sleepable also
necessitates moving the clk_set_rate() call in clock-voter.c to a
sleepable context. Do that by having clock-voter aggregate and
update the rate in prepare/unprepare instead of enable/disable
(note that enable/disable of voter clocks implicitly calls
enable/disable on the parent via generic clock code).

Now that clk_set_rate() is sleeping, call clk_prepare() and
clk_unprepare() in the clock-local code when a rate change
requires reparenting the clock. This cleans up a problem we have
where sources may be left unprepared by a clock rate switch
(hence the default true warned flag for PLLs and crystals).

Change-Id: I493a00261055001a68fa884daa52e3d281ec6a2d
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>