drm: Add an encoder and connector type enum for DPI.

drm: Add an encoder and connector type enum for DPI.

Right now exynos is exposing DPI as a TMDS encoder and VGA connector,
which seems rather misleading.  This isn't just an internal detail,
since xrandr actually exposes "VGA" as the output name.  Define some
new enums so that vc4's DPI can have a more informative name.

I considered other names for the connector as well.  For VC4, the
Adafruit DPI kippah takes the 28 GPIO pins and routes them to a
standard-ish 40-pin FPC connector, but "40-pin FPC" doesn't uniquely
identify an ordering of pins (apparently some other orderings exist),
doesn't explain things as well for the user (who, if anything, knows
their product is a DPI kippah/panel combo), and actually doesn't have
to exist (one could connect the 28 GPIOs directly to something else).
Simply "DPI" seems like a good compromise name to distinguish from the
HDMI, DSI, and TV connectors .

Signed-off-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>