Please refer to the method used for other i.MX, such in the BSP doc: uboot_mx5x.pdf.
Typically, to build u-boot for the sabre lite board, it is:
make CROSS_COMPILE=/opt/freescale/usr/local/gcc-4.1.2-glibc-2.5-nptl-3/arm-none-linux-gnueabi/bin/arm-none-linux-gnueabi- mx6q_sabrelite_config
make CROSS_COMPILE=/opt/freescale/usr/local/gcc-4.1.2-glibc-2.5-nptl-3/arm-none-linux-gnueabi/bin/arm-none-linux-gnueabi-
Other cross compiler versions should work.