including backport of mtd patches.

The general flash issue (32MB) was discussed here:
https://gist.github.com/dmke/d389bc364b3f73f525076eaee0019dc1
The resulting patch was the following:
http://lists.infradead.org/pipermail/linux-mtd/2016-December/070889.html

Another patch by nbd168 added the required mtd read operations for supporting ZBT-WG3526-32M:
https://github.com/lede-project/source/commit/22d982e#diff-3835f027e16e6416090c1833bc732af3

fixes build after 3ec63b8c

fixes #442

There is no wifi, so there is no bad wifi.

[Matthias Schiffer: rebase onto master]

[Matthias Schiffer: remove patch "ramips: simplify ubnt-erx-sfp device
definition", as it depends on other patches that have not been backported]

Needs more testing, high packet loss at the moment.