Revert "ar71xx: Use full 128MB flash on Netgear WNDR4300 and WNDR3700v4"

This reverts commit r48276.
This can overwrite the caldata_backup partition, so the layout needs to
be changed in a different way.

Thanks to Arjen de Korte for spotting the issue.

Signed-off-by: Felix Fietkau <nbd@openwrt.org>

SVN-Revision: 48456