MIPS: BCM47XX: update defconfig

The defconfig for bcm47xx contained lots of driver which are not
special for these SoCs and missed on the other side some some drivers
for parts essential for these SoC and only found on here. The flash,
usb and some Ethernet driver were missing.
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Signed-off-by: John Crispin <blogic@openwrt.org>
Patchwork: http://patchwork.linux-mips.org/patch/5930/