mtd: davinci: add support for parition binding nodes

Enhance the driver to support partition subnodes inside the nand
device bindings to describe partions on the nand device.

Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
Reviewed-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>