drm/vc4: hdmi: Add reset callback

The BCM2711 and BCM283x HDMI controllers use a slightly different reset
sequence, so let's add a callback to reset the controller.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Tested-by: Chanwoo Choi <cw00.choi@samsung.com>
Tested-by: Hoegeun Kwon <hoegeun.kwon@samsung.com>
Tested-by: Stefan Wahren <stefan.wahren@i2se.com>
Reviewed-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Link: https://patchwork.freedesktop.org/patch/msgid/a34bcb493da07eae58ed704f65e72ce0748e8952.1599120059.git-series.maxime@cerno.tech