drm/amd/display: Expose enc2_set_dynamic_metadata

[Why]
Need to implement register programming for HDR dynamic
metadata transmission and tests.

Signed-off-by: Ilya Bakoulin <Ilya.Bakoulin@amd.com>
Reviewed-by: Eric Bernstein <Eric.Bernstein@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>