powerpc: Add printk companion for ppc_md.progress

This patch adds a printk companion to replace the udbg progress function
when initmem is freed.

Suggested-by: Milton Miller <miltonm@bga.com>
Suggested-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Dave Carroll <dcarroll@astekcorp.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>