target/mips/rel6_translate: Change license to GNU LGPL v2.1 (or later)

target/mips/rel6_translate: Change license to GNU LGPL v2.1 (or later)

When adding this file and its new content in commit 3f7a927847a
("target/mips: LSA/DLSA R6 decodetree helpers") I did 2 mistakes:

1: Listed authors who haven't been involved in its development,
2: Used an incorrect GNU GPLv2 license text (using 'and' instead
   of 'or').

Instead of correcting the GNU GPLv2 license text, replace the license
by the 'GNU LGPL v2.1 or later' one, to be coherent with the other
translation files in the target/mips/ folder.

Suggested-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20210420100633.1752440-1-f4bug@amsat.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>