bnxt_en: add basic infrastructure to support PAM4 link speeds

The firmware interface has added support for new link speeds using
PAM4 modulation.  Expand the bnxt_link_info structure to closely
mirror the new firmware structures.  Add logic to copy the PAM4
capabilities and settings from the firmware.

Signed-off-by: Edwin Peer <edwin.peer@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>