drm/panel: ilitek-ili9806e: split core and DSI logic

drm/panel: ilitek-ili9806e: split core and DSI logic

Split the driver to support multiple transport buses. The core logic
(power, GPIO, backlight) is moved to a dedicated core module, while
DSI-specific code is restricted to the DSI module.

Introduce DRM_PANEL_ILITEK_ILI9806E_CORE as a hidden Kconfig symbol
selected by the bus-specific configuration.

Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patch.msgid.link/20260318073346.18041-3-dario.binacchi@amarulasolutions.com