dt-bindings: display: sun4i: Add component endpoint ID numbering scheme

The Allwinner display pipeline contains many hardware components, some
of which can consume data from one of multiple upstream components.
The numbering scheme of these components must be encoded into the device
tree so the driver can figure out which component out of two or more of
the same type it is supposed to use or program.

This patch adds the constraint that local endpoint IDs must be the index
or number of the remote endpoint's hardware block, for all components
in the display pipeline up to the TCONs.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>