lua-periphery: depend on c-periphery instead of cloning it

lua-periphery: depend on c-periphery instead of cloning it

lua-periphery currently clones and builds the c-periphery library by
itself. This 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.

This commit fixes:

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

[Peter: fix minor typo in patch 0001 description]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>