drm/vc4: hdmi: Implement finer-grained hooks

In order to prevent some pixels getting stuck in an unflushable FIFO on
bcm2711, we need to enable the HVS, the pixelvalve (the CRTC) and the HDMI
controller (the encoder) in an intertwined way, and with tight delays.

However, the atomic callbacks don't really provide a way to work with
either constraints, so we need to roll our own callbacks so that we can
provide those guarantees.

Since those callbacks have been implemented and called in the CRTC code, we
can just implement them in the HDMI driver now.

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/2e9226d971117065f3b97e597f04f7fe2f0c134c.1599120059.git-series.maxime@cerno.tech