amd-xgbe: Fix the mapping of priorities to traffic classes

The driver is checking the pfc_en field of the ieee_pfc structure to
determine whether to associate a priority with a traffic class. This is
incorrect since the pfc_en field is for determining if PFC is enabled
for a traffic class.

The association of priority to traffic class does not depend on whether
the traffic class is enabled for PFC, so remove that check. Also, the
mapping of priorities to traffic classes should be done when configuring
the traffic classes and not the PFC support so move the priority to traffic
class association from xgbe_config_dcb_pfc to xgbe_config_dcb_tc.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: David S. Miller <davem@davemloft.net>