drm/atomic: Add a function to reset connector TV properties

Commit 731514b4 upstream.
Reworked as functions have been moved from drm_atomic_helper.[c|h]
to drm_atomic_state_helper.[c|h].

During the connector reset, if that connector has a TV property, it needs
to be reset to the value provided on the command line.

Provide a helper to do that.

Reviewed-by: Noralf Trønnes <noralf@tronnes.org>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/84a7b657f09303a2850e1cc79e68f623547f3fdd.1560783090.git-series.maxime.ripard@bootlin.com