drm/panel: st7701: Add Anbernic RG28XX panel support

drm/panel: st7701: Add Anbernic RG28XX panel support

The Anbernic RG28XX is a handheld gaming device with a 2.8 inch 480x640
display. Add support for the display panel.

This panel is driven by a variant of ST7701 driver IC internally,
confirmed by dumping and analyzing its BSP initialization sequence
by using a logic analyzer. It is very similar to the existing
densitron,dmt028vghmcmi-1a panel, but differs in some unknown
register values. Besides, it is connected via SPI, so add a new entry
for the panel.

Signed-off-by: Hironori KIKUCHI <kikuchan98@gmail.com>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Reviewed-by: Jessica Zhang <quic_jesszhan@quicinc.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20240804061503.881283-6-kikuchan98@gmail.com
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240804061503.881283-6-kikuchan98@gmail.com