drm/vc4: hdmi: Move the HSM clock enable to runtime_pm

drm/vc4: hdmi: Move the HSM clock enable to runtime_pm

[ Upstream commit 411efa18e4b03840553ff58ad9b4621b82a30c04 ]

In order to access the HDMI controller, we need to make sure the HSM
clock is enabled. If we were to access it with the clock disabled, the
CPU would completely hang, resulting in an hard crash.

Since we have different code path that would require it, let's move that
clock enable / disable to runtime_pm that will take care of the
reference counting for us.

Fixes: 4f6e3d66ac52 ("drm/vc4: Add runtime PM support to the HDMI encoder driver")
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Reviewed-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210525091059.234116-3-maxime@cerno.tech
Signed-off-by: Sasha Levin <sashal@kernel.org>