dt-bindings: display: st,stm32-dsi: Remove unnecessary fields

"#address-cells" and "#size-cells" are two properties that are not
mandatory. For instance, the DSI could refer to a bridge outside the scope
of the node rather than include a 'panel@0' subnode. By doing so, address
and size fields become then unnecessary, creating a warning at build time.

Signed-off-by: Raphael Gallais-Pou <raphael.gallais-pou@foss.st.com>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Marek Vasut <marex@denx.de>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>