uboot-imx

MIPS: Use ram_top, not bi_memsize, in arch_lmb_reserve

When calculating the region to reserve for the stack in
arch_lmb_reserve, make use of ram_top instead of adding bi_memsize to
CONFIG_SYS_SDRAM_BASE. This avoids overflow if the system has enough
memory to reach the end of the address space.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>