drm/vc4: hdmi: Restore cec physical address on reconnect

Currently we call cec_phys_addr_invalidate on a hotplug deassert.
That may be due to a TV power cycling, or an AVR being switched
on (and switching edid).

This makes CEC unusable since our controller wouldn't have a physical
address anymore.

Set it back up again on the hotplug assert.

Fixes: 15b4511a

 ("drm/vc4: add HDMI CEC support")
Signed-off-by: Dom Cobley <popcornmix@gmail.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Acked-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Acked-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Tested-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Link: https://patchwork.freedesktop.org/patch/msgid/20210111142309.193441-6-maxime@cerno.tech