drm/vc4: hdmi: Store the encoder type in the variant structure

The vc4 CRTC will use the encoder type to control its output clock
muxing. However, this will be different from HDMI0 to HDMI1, so let's
store our type in the variant structure so that we can support multiple
controllers later on.

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/2736a86b498551ba9dbc5803c5bb910627a2550c.1599120059.git-series.maxime@cerno.tech