[PATCH] powerpc: Add support for changing properties from userspace

Add support to reconfigure the device tree through the existing
proc filesystem interface.  Add "add_property", "remove_property",
and "update_property" commands to the existing interface.

Signed-off-by: Dave Boutcher <sleddog@us.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>