openrisc: Consolidate setup to use memblock instead of bootmem

Clearing out one todo item. Use the memblock boot time memory
which is the current standard.

Tested-by: Guenter Roeck <linux@roeck-us.net>
Acked-by: Jonas <jonas@southpole.se>
Signed-off-by: Stafford Horne <shorne@gmail.com>