drm/vc4: hdmi: Split the interrupt handlers

The BCM2711 has two different interrupt sources to transmit and receive
CEC messages, provided through an external interrupt chip shared between
the two HDMI interrupt controllers.

The rest of the CEC controller is identical though so we need to change
a bit the code organisation to share the code as much as possible, yet
still allowing to register independent handlers.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Reviewed-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/20210111142309.193441-10-maxime@cerno.tech