All boards using the DSI node duplicate the same pattern common pattern
in board DTs, that pattern is ports with endpoint labels and the same
in-SoC regulator connection. Move that common pattern into stm32mp157.dtsi
instead.

The two boards which do define panel@0 directly in the DSI bridge node now
have #address-cells/#size-cells in their board DT instead of it being in
stm32mp157.dtsi and activated incorrectly for all boards, even the ones
which use e.g. another DSI-to-something bridge.
Signed-off-by: Marek Vasut <marex@denx.de>
Acked-by: Raphaël Gallais-Pou <raphael.gallais-pou@foss.st.com>
Signed-off-by: Alexandre Torgue <alexandre.torgue@foss.st.com>