drm: add clone mode check for CRTC

Add a common helper to check if the given CRTC state is in clone mode.
This can be used by drivers to help detect if a CRTC is being shared by
multiple encoders

Signed-off-by: Jessica Zhang <quic_jesszhan@quicinc.com>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Reviewed-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20241216-concurrent-wb-v4-1-fe220297a7f0@quicinc.com


Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>