grep: upgrade to 2.15

Signed-off-by: Cristiana Voicu <cristiana.voicu@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
grep: upgrade to 2.16

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
grep: upgrade from 2.16 to 2.18

Upgrade grep from 2.16 to 2.18.

Signed-off-by: Chen Qi <Qi.Chen@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>