dt-bindings: Add vendor prefix for Ronbo Electronics

Ronbo Electronics manufactures display panels.

Reviewed-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Signed-off-by: Konstantin Sudakov <k.sudakov@integrasources.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/a7ab8bd59ad673f88e2c39cf6cb21bd959cf4db4.1550650810.git-series.maxime.ripard@bootlin.com