drm/tests: Add tests for the new Monochrome value of tv_mode

Adds test for the cmdline parser, connector property, and
drm_analog_tv_mode to ensure the behaviour of the new value is
correct.

Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Signed-off-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240620110947.3615207-1-dave.stevenson@raspberrypi.com