c-periphery: new package

This package is needed as a dependency of lua-periphery. Currently,
c-periphery is automatically cloned by lua-periphery, which causes two
problems:

 1/ It does not integrate properly with the download infrastructure of
    Buildroot, making offline builds impossible since not the entire
    source code is downloaded by Buildroot.

 2/ It does not use the latest version of c-periphery, which has some
    fixes contributed by Vicente to fix c-periphery on MIPS.

Introducing this package is needed as part of the fix for the
following build failure:

  http://autobuild.buildroot.org/results/0ad/0ad656970b3cbc84b5531b28155ba2f747715fe3/



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>