openssh: Improve LICENSE to show BSD license variants.

Update LICENSE to show that BSD-2-Clause, BSD-3-Clause and BSD-4-Clause
are all present.

(From OE-Core rev: d1793895)

Signed-off-by: Wang Mingyu <wangmy@cn.fujitsu.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Mikko Rapeli <mikko.rapeli@bmw.de>
(cherry picked from commit e42870e233a85bc0d55395ef110b7445dfe784f8)
Signed-off-by: Steve Sakoman <steve@sakoman.com>