octeontx2-af: Skip CGX/RPM probe incase of zero lmac count

In few error cases MAC(CGX/RPM) block is having 0 lmacs.
AF driver uses MAC block with lmac pair to get firmware
data etc. These commands will fail as there is no LMAC
associated with MAC block.

This patch skips the probe of these MAC blocks such that AF driver
uses correct MAC block and LMAC pair for firmware communication and
define new LMAC_AF_ERROR types for command timeout etc.

This patch also enables channel back pressure for all LMACs.

Signed-off-by: Hariprasad Kelam <hkelam@marvell.com>
Signed-off-by: Sunil Kovvuri Goutham <sgoutham@marvell.com>
Signed-off-by: Geetha sowjanya <gakula@marvell.com>
Signed-off-by: David S. Miller <davem@davemloft.net>