MIPS: Let early memblock_alloc*() allocate memories bottom-up

MIPS: Let early memblock_alloc*() allocate memories bottom-up

After switched to NO_BOOTMEM, there are several boot failures. Some of
them have been fixed and some of them haven't. I find that many of them
are because of memory allocations are top-down, while the old behavior
is bottom-up. This patch let early memblock_alloc*() allocate memories
bottom-up to avoid some potential problems.

Signed-off-by: Huacai Chen <chenhc@lemote.com>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Fixes: bcec54bf3118 ("mips: switch to NO_BOOTMEM")
Patchwork: https://patchwork.linux-mips.org/patch/21069/
References: https://patchwork.linux-mips.org/patch/21031/
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: James Hogan <james.hogan@mips.com>
Cc: Steven J . Hill <Steven.Hill@cavium.com>
Cc: linux-mips@linux-mips.org
Cc: Fuxin Zhang <zhangfx@lemote.com>
Cc: Zhangjin Wu <wuzhangjin@gmail.com>