media: allegro: add pm_runtime support

The allegro driver must ensure that the mcu and core clocks are enabled
and set to the expected clock rate before trying to load the firmware
and to reset the MCU.

Up until now, the driver assumed that the clocks are always enabled in
the PL (programming logic), because the xlnx_vcu driver did not export
the clocks to other drivers. This has changed and by explicitly enabling
the clocks in the driver, this assumption can be dropped.

It might even be possible to disable the clocks for the encoder if the
encoder is not used. However, the behavior is not documented and it
might be necessary to reinitialize the encoder after deactivating the
clocks. Play it safe by sticking to the current behavior.

Signed-off-by: Michael Tretter <m.tretter@pengutronix.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>