octeontx2-af: Bringup CGX LMAC links by default

- Added new CGX firmware interface API for sending link up/down
  commands

- Do link up for cgx lmac ports by default at the time of CGX
  driver probe. Since cgx link up in driver probe affects the
  Linux boot time, linkup procedure is kept threaded using
  workqueues.
  For this, a new cgx API cgx_lmac_linkup_start has been added.

Signed-off-by: Linu Cherian <lcherian@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>