MIPS: BCM47XX: select BOOT_RAW

All the boot loaders I have seen are booting the kernel in raw mode by
default. CFE seems to support elf kernel images too, but the default
case is raw for the devices I know of. Select this option to make the
kernel boot on most of the devices with the default options.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Patchwork: http://patchwork.linux-mips.org/patch/4746/
Signed-off-by: John Crispin <blogic@openwrt.org>