dt-bindings: Add Pervasive Displays RePaper bindings

Add device-tree binding documentation for the 1.44", 1.9", 2.0" and 2.7"
display panels.

Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1496934875-51984-3-git-send-email-noralf@tronnes.org