dt-bindings: Add DT bindings for Toshiba TC358762 DSI-to-DPI bridge

Add DT bindings for Toshiba TC358762 DSI-to-DPI bridge, this
one is used in the Raspberry Pi 7" touchscreen display unit.

Signed-off-by: Marek Vasut <marex@denx.de>
Reviewed-by: Rob Herring <robh@kernel.org>
Cc: dri-devel@lists.freedesktop.org
Cc: Eric Anholt <eric@anholt.net>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: devicetree@vger.kernel.org
Signed-off-by: Sam Ravnborg <sam.ravnborg@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200809105705.6334-1-marex@denx.de