drm/tiny/repaper: Make driver OF-independent

There is one OF call in the driver that limits its area of use.
Replace it to generic device_get_match_data() and get rid of OF dependency.

While here, cast SPI driver data to certain enumerator type.

Cc: Noralf Trønnes <noralf@tronnes.org>
Cc: dri-devel@lists.freedesktop.org
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: David Lechner <david@lechnology.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200131204923.48928-1-andriy.shevchenko@linux.intel.com