Extend the block i/o system to allow registered devices to advertise an erase geometry. Devices which do not need to be explicitly erased may skip this. Extent the Zynq spiflash code to publish the erase geometry as read from the flash device. Signed-off-by: John Grossman <johngro@google.com> Change-Id: I42e16fbe9a0fcf8334c317f16dea1c551c203eb2