MIPS: BCM63XX: add flash detection for BCM6362

BCM6362 support booting from SPI flash and NAND.

Signed-off-by: Jonas Gorski <jogo@openwrt.org>
Patchwork: http://patchwork.linux-mips.org/patch/5012/


Acked-by: John Crispin <blogic@openwrt.org>