drm/sun4i: tcon: Pass drm_encoder * into sun4i_tcon0_mode_set_cpu

drm/sun4i: tcon: Pass drm_encoder * into sun4i_tcon0_mode_set_cpu

sun4i_tcon0_mode_set_cpu() currently accepts struct mipi_dsi_device *
as its second parameter. This is derived from drm_encoder.

The DSI encoder is tied to the CPU interface mode of the TCON as a
special case. In theory, if hardware were available, we could also
support normal CPU interface modes. It is better to pass the generic
encoder instead of the specialized mipi_dsi_device, and handle the
differences inside the function.

Passing the encoder would also enable the function to pass it, or any
other data structures related to it, to other functions expecting it.
One such example would be dithering support that will be added in a
later patch, which looks at properties tied to the connector to
determine whether dithering should be enabled or not.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180907041948.19913-2-wens@csie.org