drm/panel: raydium-rm67200: Move initialization from enable() to prepare stage

The DSI host has different modes in prepare() and enable() functions,
prepare() is in LP command mode and enable() is in HS video mode.

>From our experience, generally the initialization sequence needs to be
sent in the LP command mode.

Move the setup init function from enable() to prepare() to fix a display
shift on rk3568 evb.

Tested on rk3568/rk3576/rk3588 EVB.

Signed-off-by: Andy Yan <andy.yan@rock-chips.com>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://lore.kernel.org/r/20250618091520.691590-1-andyshrk@163.com