dsa: mv88e6xxx: Move available stats into info structure

dsa: mv88e6xxx: Move available stats into info structure

Different families of switches have different statistics available.
This information is current hard coded into functions, however this
information will also soon be needed when getting statistics from the
RMU. Move it into the info structure.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20241207-v6-13-rc1-net-next-mv88e6xxx-stats-refactor-v1-1-b9960f839846@lunn.ch
Signed-off-by: Jakub Kicinski <kuba@kernel.org>