libmad: add Thumb2 patches from Debian

This fixes recurrent libmad build failures reported by the
autobuilder. See:

  http://autobuild.buildroot.net/results/a10c943e74b6e67e69183a35b5762482e357a75f/build-end.log



Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>