ixgbe: DCB, abstract out dcb_config from DCB hardware configuration

Currently the routines that configure the HW for DCB require a
ixgbe_dcb_config structure. This structure was designed to support
the CEE standard and does not match the IEEE standard well.

This patch changes the HW routines in ixgbe_dcb_8259x.{ch} to use
raw pfc and bandwidth values. This requires some parsing of the DCB
configuration but makes the HW routines independent of the data
structure that contains the DCB configuration.

The primary advantage to doing this is we can do HW setup directly
from the 802.1Qaz ops without having to arbitrarily encapsulate this
data into the CEE structure.

Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
Tested-by: Ross Brattain <ross.b.brattain@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>