sfc: Clean up struct falcon_board and struct falcon_board_data

Put all static information in struct falcon_board_type and replace it
with a pointer in struct falcon_board.  Simplify probing aocordingly.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>