drm/tinydrm: Move tinydrm_display_pipe_init() to mipi-dbi

tinydrm_display_pipe_init() has only one user now, so move it to mipi-dbi.

Changes:
- Remove drm_connector_helper_funcs.detect, it's always connected.
- Store the connector and mode in mipi_dbi instead of it's own struct.

Otherwise remove some leftover tinydrm-helpers.h inclusions.

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>
Link: https://patchwork.freedesktop.org/patch/msgid/20190719155916.62465-12-noralf@tronnes.org