common/sfc_efx/base: add API to get Rx prefix information

common/sfc_efx/base: add API to get Rx prefix information

Define default Siena, EF10 default, packed stream, equal-stride
superbuffer and Riverhead default prefixes in order to make an API
to get Rx prefix layout information generic and usable on all NICs.

Riverhead supports many Rx prefixes. Riverhead FW supports MCDI to
choose Rx prefix based on required Rx prefix fields and allows to
query the prefix layout using MCDI. The patch prepares to introduce
the support in libefx and provides fallback for NICs and FW which
lacks the support.

Signed-off-by: Andrew Rybchenko <arybchenko@solarflare.com>
Reviewed-by: Andy Moreton <amoreton@xilinx.com>