elfutils: Update license information

elfutils: Update license information

Update license information for overall package, package libraries, and
package utilities in the recipe to match the license information as
described on the upstream website [1]:

"License. The libraries and backends are dual GPLv2+/LGPLv3+. The
utilities are GPLv3+."

[1] https://sourceware.org/elfutils

Signed-off-by: William Lyu <William.Lyu@windriver.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>