common/sfc_efx/base: add match spec init/fini APIs

common/sfc_efx/base: add match spec init/fini APIs

An MAE rule is a function of match criteria and a priority. The said match
criteria have to be provided using "mask-value pairs" packing format which
on its own should not be exposed to client drivers. The latter have to use
a functional interface of sorts in order to generate a match specification.

Define an EFX match specification and implement initialise / finalise APIs.
The "mask-value pairs" buffer itself is not used in this particular patch,
so the corresponding struct member will be added in the follow-up patch.

Signed-off-by: Ivan Malov <ivan.malov@oktetlabs.ru>
Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>
Reviewed-by: Andy Moreton <amoreton@xilinx.com>