drm/panel: st7701: Add support for SPI for configuration

drm/panel: st7701: Add support for SPI for configuration

The ST7701 supports not only MIPI DSI, but also SPI as an interface
for configuration. To support a panel connected via SPI with an RGB
parallel interface, add support for SPI using MIPI DBI helpers.

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/20240804061503.881283-5-kikuchan98@gmail.com
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240804061503.881283-5-kikuchan98@gmail.com