drm/vc4: hdmi: Add container_of macros for encoders and connectors

Whenever the code needs to access the vc4_hdmi structure from a DRM
connector or encoder, it first accesses the drm_device associated to the
connector, then retrieve the drm_dev private data which gives it a
pointer to our vc4_dev, and will finally follow the vc4_hdmi pointer in
that structure.

That will also give us some trouble when having multiple controllers,
but now that we have our encoder and connector structures that are part
of vc4_hdmi, we can simply call container_of on the DRM connector or
encoder and retrieve the vc4_hdmi structure directly.

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: Eric Anholt <eric@anholt.net>
Link: https://patchwork.freedesktop.org/patch/msgid/536ecce5898ea75839fa3788b876009d69a5ccae.1599120059.git-series.maxime@cerno.tech