net/sfc: maintain controller to EFX interface mapping

net/sfc: maintain controller to EFX interface mapping

Newer hardware may have arbitrarily complex controller configurations,
and for this reason the mapping has been made dynamic: it is represented
with a dynamic array that is indexed by controller numbers and each
element contains an EFX interface number. Since the number of controllers
is expected to be small, this approach should not hurt the performance.

Signed-off-by: Viacheslav Galaktionov <viacheslav.galaktionov@oktetlabs.ru>
Signed-off-by: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
Reviewed-by: Andy Moreton <amoreton@xilinx.com>