Revert "Revert "nvram: increase NVRAM size to 64 KiB""

Revert "Revert "nvram: increase NVRAM size to 64 KiB""

This reverts commit r45579.

With the latest change r46251 ("nvram: fix "Segmentation fault" caused
by setting memory out of buffer") nvram utility shouldn't crash anymore.

It was tested on 3 brcm47xx devices:
1) Unknown with 0x10000 NVRAM size (0x8000 offset)
2) Linksys E1000 V2.1 with 0x10000 (0x8000 offset)
3) Linksys WRT300N V1 with 0x10000 (0x8000 offset)

And 3 bcm53xx devices:
1) Buffalo WZR-600DHP2 with 0x160000 NVRAM size
2) Buffalo WZR-1750DHP with 0x10000 NVRAM size
3) Netgear R6250 V1 with 0x180000 NVRAM size
(all using 0 offset)

This is an important change as it allows reading whole NVRAM. This may
critical when reading some basic configuration (e.g. switch ports).

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Backport of r46253

git-svn-id: svn://svn.openwrt.org/openwrt/branches/chaos_calmer@46259 3c298f89-4303-0410-b956-a3cf2f4a3e73