dfu: defer parsing of device string to IO backend

Devices are not all identified by a single integer. To support
this, defer the parsing of the device string to the IO backed, so that
it can apply the appropriate rules.

SPI devices are specified as controller:chip_select. SPI/SF support will
be added soon.

MMC devices can also be specified as controller[.hwpart][:partition] in
many commands, although we don't support that syntax in DFU.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
diff --git a/drivers/dfu/dfu_nand.c b/drivers/dfu/dfu_nand.c
index e1c9a88..f9ee189 100644
--- a/drivers/dfu/dfu_nand.c
+++ b/drivers/dfu/dfu_nand.c
@@ -179,7 +179,7 @@
 	return DFU_DEFAULT_POLL_TIMEOUT;
 }
 
-int dfu_fill_entity_nand(struct dfu_entity *dfu, char *s)
+int dfu_fill_entity_nand(struct dfu_entity *dfu, char *devstr, char *s)
 {
 	char *st;
 	int ret, dev, part;