drm/mipi_dbi: Use drmm_add_final_kfree in all drivers

They all share mipi_dbi_release so we need to switch them all
together. With this we can drop the final kfree from the release
function.

Aside, I think we could perhaps have a tiny additional helper for
these mipi_dbi drivers, the first few lines around devm_drm_dev_init
are all the same (except for the drm_driver pointer).

Acked-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Noralf Trønnes <noralf@tronnes.org>
Tested-by: Noralf Trønnes <noralf@tronnes.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Eric Anholt <eric@anholt.net>
Cc: David Lechner <david@lechnology.com>
Cc: Kamlesh Gurudasani <kamlesh.gurudasani@gmail.com>
Cc: "Noralf Trønnes" <noralf@tronnes.org>
Cc: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200323144950.3018436-6-daniel.vetter@ffwll.ch