This moves mipi-dbi to be a core helper with the name drm_mipi_dbi.

Fixup include's in drivers.
Move the docs entry and delete tinydrm.rst.
Delete the last tinydrm todo entry.

v2: Make DRM_MIPI_DBI tristate to enable it being built as a module.

Cc: Eric Anholt
Cc: David Lechner
Reviewed-by: Sam Ravnborg
Signed-off-by: Noralf Trønnes
Acked-by: David Lechner
Acked-by: Eric Anholt
Link: https://patchwork.freedesktop.org/patch/msgid/20190722104312.16184-9-noralf@tronnes.org