drm/amd/pm: workaround for audio noise issue

drm/amd/pm: workaround for audio noise issue

commit 9d03730ecbc5afabfda26d4dbb014310bc4ea4d9 upstream.

On some Intel platforms, audio noise can be detected due to
high pcie speed switch latency.
This patch leaverages ppfeaturemask to fix to the highest pcie
speed then disable pcie switching.

v2:
coding style fix

Signed-off-by: Kenneth Feng <kenneth.feng@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>