MIPS: BCM47XX: add bcm47xx prefix in front of nvram function names

The nvram functions are exported and used by some normal drivers. To
prevent name clashes with ofter parts of the kernel code add a bcm47xx_
prefix in front of the function names and the header file name.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Patchwork: http://patchwork.linux-mips.org/patch/4744/
Signed-off-by: John Crispin <blogic@openwrt.org>