package/sg3_utils: link with libatomic when needed

sg3_utils uses __atomic_fetch_add_4 since version 1.45 and
https://github.com/hreinecke/sg3_utils/commit/e9445f4efc012d37809342ba21f16360a0208f06

Fixes:
 - http://autobuild.buildroot.org/results/7773ead32375ca9073f45db83dac299aa2edd619



Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>