drm/vc4: hdmi: Depends on CONFIG_PM

We already depend on runtime PM to get the power domains and clocks for
most of the devices supported by the vc4 driver, so let's just select it
to make sure it's there.

Link: https://lore.kernel.org/r/20220629123510.1915022-38-maxime@cerno.tech
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Tested-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>