MIPS: BCM47XX: Make ssb init NVRAM instead of bcm47xx polling it

This makes NVRAM code less bcm47xx/ssb specific allowing it to become a
standalone driver in the future. A similar patch for bcma will follow
when it's ready.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Acked-by: Hauke Mehrtens <hauke@hauke-m.de>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/7612/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>