dt-bindings: display: bridge: tc358762: Document reset-gpios

This chip has one reset GPIO input, document it. The reset GPIO
is optional as it is sometimes not connected on some hardware.

Signed-off-by: Marek Vasut <marex@denx.de>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Robert Foss <rfoss@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230530192805.648646-1-marex@denx.de