drm/panel: s6e63m0: Switch to DBI abstraction for SPI

The SPI access to s6e63m0 is using the DBI protocol, so switch
to using the elaborate DBI protocol implementation in the DRM
DBI helper library.

Acked-by: Noralf Trønnes <noralf@tronnes.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20210614181135.1124445-2-linus.walleij@linaro.org