powerpc/40x: Add APM8018X SOC support

The AppliedMicro APM8018X embedded processor targets embedded applications that
require low power and a small footprint. It features a PowerPC 405 processor
core built in a 65nm low-power CMOS process with a five-stage pipeline executing
up to one instruction per cycle. The family has 128-kbytes of on-chip memory,
a 128-bit local bus and on-chip DDR2 SDRAM controller with 16-bit interface.

Signed-off-by: Tanmay Inamdar <tinamdar@apm.com>
Signed-off-by: Josh Boyer <jwboyer@gmail.com>