drm/vc4: crtc: Rename HDMI encoder type to HDMI0

The previous generations were only supporting a single HDMI controller, but
that's about to change, so put an index as well to differentiate between
the two controllers.

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/84e11e4793aaa30d6e5c56e305d22404ac5a932d.1599120059.git-series.maxime@cerno.tech