drm/amd/display: Add debugfs interface for ODM combine info

[Why]
For use with IGT tests in userspace, the number of ODM segments in use
is required to be exposed to userspace to verify that ODM Combine is
working as expected when special timings are committed.

[How]
Add a connector specific debugfs entry that prints the number of ODM
segments in use.

Reviewed-by: Wenjing Liu <wenjing.liu@amd.com>
Acked-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>