LICENSES: Add LGPL 2.1 license

This is used in util/cbfstool/elf.h and lzmadecode.

Change-Id: I75e71259f23bee602ffb54b0c51e0e4a9da3f8e5
Signed-off-by: Martin Roth <[email protected]>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/80584
Tested-by: build bot (Jenkins) <[email protected]>
Reviewed-by: Felix Singer <[email protected]>

Author: martinlroth