msm: pil-venus: Move the GDSC control out of PIL driver

The PIL driver has full control of the Venus GDSC. It turns
on the GDSC when booting up venus and leaves it on until
venus is shutdown.

In order to save more power during video playback, interframe
power collapse can be used. This requires that the GDSC can be
turned on/off during video playback.

In order to allow the Venus driver to turn on/off the GDSC, the
PIL driver should no longer hold the GDSC on throughout the time
Venus is booted up. It is safe to do so since the Venus driver
has already added GDSC control.

Note that the proxy voting of GDSC is still present solely for
the purpose of allowing standalone testing of the Venus PIL
driver.

Change-Id: I49b7331d4ec40c08b1eba0a72942564899ca4b8f
Signed-off-by: Tianyi Gou <tgou@codeaurora.org>