dt-bindings: restrict properties for sitronix,st7735r

David Lechner noticed (paraphrased):
- not all properties from panel-common are applicable.
- missing optional rotation and backlight properties

Fix this by listing all allowed properties,
and do not allow other properties.

Fixes: abdd9e37 ("dt-bindings: display: sitronix,st7735r: Convert to DT schema")
Reported-by: David Lechner <david@lechnology.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Rob Herring <robh@kernel.org>
Cc: David Lechner <david@lechnology.com>
Cc: dri-devel@lists.freedesktop.org
Link: https://patchwork.freedesktop.org/patch/msgid/20200120190249.GA9619@ravnborg.org