defconfigs: all use the headers from the kernel

For most defconfigs, it was trivial to deduce the kernel version, by
just reading the version string, which could be:
  - a standard upstream version string vX.Y.Z
  - a non-standard version string, but still containg the standard X.Y.Z

Those for which it was not so trivial were those hosted on git tree.
Since most were already using a custom linux-headers version, it could
be easily deduced from that. It was confirmed by browsing said git trees
and check the version there.

There are a few cases were there was a mismatch:

  - microzed:     uses a 3.18 kernel, but 3.8 headers; fixed.
  - xilinx_zc706: uses a 3.14 kernel, but 3.8 headers; fixed.
  - zedboard:     uses a 3.18 kernel, but 3.8 headers; fixed.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Cc: Peter Korsgaard <peter@korsgaard.com>
Cc: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>