drm/tests: hdmi: Add limited range tests for YUV420 mode

drm/tests: hdmi: Add limited range tests for YUV420 mode

Provide tests to verify that drm_atomic_helper_connector_hdmi_check()
helper behaviour when using YUV420 output format is to always set the
limited RGB quantization range to 'limited', no matter what the value of
Broadcast RGB property is.

Acked-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
Link: https://lore.kernel.org/r/20250527-hdmi-conn-yuv-v5-15-74c9c4a8ac0c@collabora.com
Signed-off-by: Maxime Ripard <mripard@kernel.org>