drm/amd/display: Add helper to convert DC status

During the debugging process related to a hot-plug
problem with 4k display, we realized that we had
some issues related to the global state validation.
This problem was not explicitly highlighted in the
dmesg log, for this reason, this commit adds a function
that converts `enum dc_status` to a human-readable
string and appends the proper warning message in case
of failure.

Signed-off-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Reviewed-by: Harry Wentland <Harry.Wentland@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>