nvram: get rid of NVRAM_SPACE

Now we support NVRAM whatever its size is.

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

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@46262 3c298f89-4303-0410-b956-a3cf2f4a3e73