ipq806x: update target to v3.18

Patches in the ipq806x/patches folder were out of tree in v3.14. The
newest patch at the time was from June, so we can safely assume that
either the patches have been merged, or they have been rejected for
a good reason. If patches are seen missing, we'll cherry-pick them
on a per-needed basis.

This new kernel have been tested on AP148, which seems to works fine.

Signed-off-by: Mathieu Olivari <mathieu@codeaurora.org>

SVN-Revision: 44386