[MIPS] Fix sparsemem support.

Move memory_present() in arch/mips/kernel/setup.c. When using sparsemem
extreme, this function does an allocate for bootmem. This would always
fail since init_bootmem hasn't been called yet.

Move memory_present after free_bootmem. This only marks actual memory
ranges as present instead of the entire address space.

Signed-off-by: Chad Reese  <creese@caviumnetworks.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>