[lib][bio] Add erase geometry to lib/bio

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

platform/armemu/blkdev.c

@@ -78,7 +78,7 @@ void platform_init_blkdev(void)
 	if (get_blkdev_len() == 0)
 		return;
 
-	bio_initialize_bdev(&dev, "block0", 512, get_blkdev_len() / 512);
+	bio_initialize_bdev(&dev, "block0", 512, get_blkdev_len() / 512, 0, NULL);
 
 	// fill in hooks
 	dev.read_block = &read_block;