Needed this myself. Just need to ask Linino "nicely".
root@arduino:/# dmesg | grep tty
[ 0.000000] Kernel command line: board=Linino console=ttyATH0,250000 mtdparts=spi0.0:256k(u-boot)ro,64k(u-boot-env)ro,14656k(rootfs),1280k(kernel),64k(nvram),64k(art),15936k@0x50000(firmware) rootfstype=squashfs,jffs2 noinitrd
[ 0.620000] ar933x-uart: ttyATH0 at MMIO 0x18020000 (irq = 11) is a AR933X UART
[ 0.630000] console [ttyATH0] enabled, bootconsole disabled
Found this by searching through the OpenWRT forums.