ok I did smth like this : (using tftp server on 10.103.33.88 )
-load raw 0xa0208000 1575336 /tftp/10.103.33.88:zImage
-exec 0xa0208000 "noinitrd console = ttymxc0, 115200 root=/dev/nfs nfsroot=10.103.33.88:/tftpboot/libt/ init=/linuxrc ip=10.103.33.89:10.103.32.1"
it's not yet perfect, but it's load the file correctly, but freez during decompressing.
if it could help someone.