MIPS: BCM47XX: Increase NVRAM buffer size to 64 KiB

For years Broadcom devices use 64 KiB NVRAM partition size and some of
them indeed have it filled in more than 50%. This change allows reading
whole NVRAM e.g. on Netgear WNDR4500 and Netgear R8000.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: Hauke Mehrtens <hauke@hauke-m.de>
Patchwork: https://patchwork.linux-mips.org/patch/9651/


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