regulator: dt-bindings: rpi-panel: Add regulator for 7" Raspberry Pi 720x1280

regulator: dt-bindings: rpi-panel: Add regulator for 7" Raspberry Pi 720x1280

Document regulator compatible string for the 7" Raspberry Pi 720x1280 DSI
panel based on ili9881. This is the Raspberry Pi DSI Panel V2. The newer
Raspberry Pi 5" and 7" panels have a slightly different register map to
the original one and offers PWM backlight control.

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Link: https://patch.msgid.link/20250609000748.1665219-1-marek.vasut+renesas@mailbox.org
Signed-off-by: Mark Brown <broonie@kernel.org>