gnu: Add AVRDUDE

* gnu/packages/avrdude.scm: New file
* gnu-system.am (GNU_SYSTEM_MODULES): Add avrdude.scm
* gnu/packages/patches/avrdude-fix-libusb.patch: New patch.
* gnu-system.am (dist_patch_DATA): Add it.

Signed-off-by: Ludovic Courtès <ludo@gnu.org>