kernel: b53: add initial support for switches in BCM5301X

This is also known as BCM470{7,8,9}.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>


git-svn-id: svn://svn.openwrt.org/openwrt/trunk@38712 3c298f89-4303-0410-b956-a3cf2f4a3e73