drm/tinydrm: Split struct mipi_dbi in two

Split struct mipi_dbi into an interface part and a display pipeline part.
The interface part can be used by drivers that need to initialize the
controller, but that won't upload the framebuffer over this interface.

MIPI DBI supports 3 interface types:
- A. Motorola 6800 type parallel bus
- B. Intel 8080 type parallel bus
- C. SPI type with 3 options:

I've embedded the SPI type specifics in the mipi_dbi struct to avoid
adding unnecessary complexity. If more interface types will be supported
in the future, the type specifics might have to be split out.

Rename functions to match the new struct mipi_dbi_dev:
- drm_to_mipi_dbi() -> drm_to_mipi_dbi_dev().
- mipi_dbi_init*() -> mipi_dbi_dev_init*().

Cc: Eric Anholt <eric@anholt.net>
Cc: David Lechner <david@lechnology.com>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Acked-by: David Lechner <david@lechnology.com>
Acked-by: Eric Anholt <eric@anholt.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20190722104312.16184-5-noralf@tronnes.org