b53: Allow using all 8 ports on BCM53011

On two tested devices: Netgear R6250 (BCM53011 rev 2) and Luxul XWC-1000
(BCM53011 rev 3) it was possible to use port 7 and eth1 (instead of port
5 and eth0). It seems BCM53011 just like BCM53012 has 8 ports and
usually 3 of them are connected to the SoC.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@46104 3c298f89-4303-0410-b956-a3cf2f4a3e73