Add device tree support to the emc driver, filling in the platform data
based on the DT bindings.

Changes since v1:

* Unmangled some messed up patch squashes, moving changes to earlier patches
* Flipped an of_property_read_u32 return value test
* Clarified clock settings message on case where no table is provided
Signed-off-by: Olof Johansson <olof@lixom.net>
Acked-by: Stephen Warren <swarren@nvidia.com>