sfc: Add permissions to MCDI commands

There is one primary function per adaptor, one link control function
per port and the rest as categorised as general.

This patch adds privileges to the MCDI commands based on which
functions are allowed to call them.

Signed-off-by: Shradha Shah <sshah@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>