drm/amd/display: Fix deadlock when falling back to v2 from v3

[Why]
A deadlock in the kernel occurs when we fallback from the V3 to V2
add_topology_to_display or remove_topology_to_display because they
both try to acquire the dtm_mutex but recursive locking isn't
supported on mutex_lock().

[How]
Make the mutex_lock/unlock more fine grained and move them up such that
they're only required for the psp invocation itself.

Fixes: bf62221e

 ("drm/amd/display: Add DCN3.1 HDCP support")

Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Aric Cyr <aric.cyr@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org