dt-bindings: display: panel: Add ilitek ili9341 panel bindings

Add documentation for "ilitek,ili9341" panel.

Signed-off-by: Dillon Min <dillon.minfei@gmail.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/lkml/1626853288-31223-2-git-send-email-dillon.minfei@gmail.com/
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/1627098243-2742-2-git-send-email-dillon.minfei@gmail.com