powerpc/44x: Support OCM(On Chip Memory) for APM821xx SoC and Bluestone board

This patch consists of:
- Add driver for OCM component
- Export OCM Information at /sys/kernel/debug/ppc4xx_ocm/info

Signed-off-by: Vinh Nguyen Huu Tuong <vhtnguyen@apm.com>
Acked-by: Josh Boyer <jwboyer@gmail.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>