drm/vc4: encoder: Add finer-grained encoder callbacks

In the BCM2711, the setup of the HVS, pixelvalve and HDMI controller
requires very precise ordering and timing that the regular atomic callbacks
don't provide. Let's add new callbacks on top of the regular ones to be
able to split the configuration as needed.

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/1dd78efe8f29add73c97d0148cfd4ec8e34aaf22.1599120059.git-series.maxime@cerno.tech