uboot-phytec

nios2: enlarge the code relocation range

As we will use u-boot-dtb.bin, the code relocation range
should be adjusted to accommodate the additional dtb.
It might be overkilled to look into dtb header to find the
dtb size, so we will simply use CONFIG_SYS_MONITOR_LEN.

Signed-off-by: Thomas Chou <thomas@wytron.com.tw>