sh_eth: remove mask fields from 'struct bb_info'

The MDIO control bits are always mapped to the same bits of the same register
(PIR), so there's no need to store their masks in the 'struct bb_info'...

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Acked-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: David S. Miller <davem@davemloft.net>