common/sfc_efx/base: support unprivileged MAE clients

In order to differentiate between privileged and unprivileged MAE clients,
add a separate boolean flag to represent a NIC's MAE privilege level.

Allow initializing unprivileged MAE clients by avoiding calls to functions
that can only be called by the admin NIC.

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>