[MIPS] IP27: Fix bootmem memory setup

Changes in the generic bootmem code broke memory setup for IP27. This
patch fixes this by replacing lots of special IP27 code with generic
bootmon code. This has been tested only on a single node.

Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>