gnu: libftdi: Fix mistakes in package description.

* gnu/packages/libftdi.scm (libftdi): Change 'libusb' from a
  'native-input' to a normal 'input'.  Fix the 'home-page' and
  'license' fields.

gnu: Add libftdi.

* gnu/packages/libftdi.scm: New file
* gnu-system.am (GNU_SYSTEM_MODULES): Add libftdi.scm

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