bootargs=mem=38M console=ttyAMA0,115200 root=/dev/mtdblock2 rootfstype=cramfs mtdparts=xm_sfc:256K(boot),1536K(kernel),2560K(romfs),2816K(user),1024K(mtd)
I have bit different bootargs with image built with SDK.
Also with xmuart=0 I got serial console working.