hw/mips/boston: Fix Lesser GPL version number

hw/mips/boston: Fix Lesser GPL version number

There is no "version 2" of the "Lesser" General Public License.
It is either "GPL version 2.0" or "Lesser GPL version 2.1".
This patch replaces all occurrences of "Lesser GPL version 2" with
"Lesser GPL version 2.1" in comment section.

Signed-off-by: Chetan Pant <chetan4windows@gmail.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20201023122633.19466-1-chetan4windows@gmail.com>
[PMD: Added hw/mips/ prefix in subject]
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>