Export memset for standalone AQ FW load apps

The 'commit 95279315 ("board/ls2085rdb: Export functions for
standalone AQ FW load apps")' mentioned memset was exported but
it was not, this patch exports the memset.

Signed-off-by: Shaohui Xie <Shaohui.Xie@nxp.com>
Signed-off-by: Gong Qianyu <Qianyu.Gong@nxp.com>
Reviewed-by: York Sun <york.sun@nxp.com>