drm/probe-helper: Provide a TV get_modes helper

drm/probe-helper: Provide a TV get_modes helper

Most of the TV connectors will need a similar get_modes implementation
that will, depending on the drivers' capabilities, register the 480i and
576i modes.

That implementation will also need to set the preferred flag and order
the modes based on the driver and users preferrence.

This is especially important to guarantee that a userspace stack such as
Xorg can start and pick up the preferred mode while maintaining a
working output.

Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Tested-by: Mateusz Kwiatkowski <kfyatek+publicgit@gmail.com>
Acked-in-principle-or-something-like-that-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://lore.kernel.org/r/20220728-rpi-analog-tv-properties-v10-12-256dad125326@cerno.tech
Signed-off-by: Maxime Ripard <maxime@cerno.tech>