package/libftdi1: fix license

package/libftdi1: fix license

The GPL only applies to the C++ bindings and eeprom utility, which are
conditionally enabled with BR2_PACKAGE_LIBFTDI1_LIBFTDIPP1 and
BR2_PACKAGE_LIBFTDI1_FDTI_EEPROM, respectively.

The COPYING.LIB is indeed the LGPL-2.0, but the source file for
libftdi1 states LGPL-2.1-only, see src/ftdi.c

The src/ftdi_stream.c also bears a notice of the MIT license, so the
library itself is under both LGPL-2.1-only and MIT.

Note: the COPYING.GPL license file may get added twice to the list, but
that is not a problem in practice: it is just copied twice.

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
[yann.morin.1998@free.fr:
  - GPL-2.0 also applies to the ftdi_eeprom utility
  - s/ftdipp1/libftdipp1/
]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>