bootstd: Add bootflow_iter_check_mmc() helper

Some bootflows might be able to only boot from MMC devices.

Add a helper function these bootflows can use.

Reviewed-by: Igor Opaniuk <igor.opaniuk@gmail.com>
Reviewed-by: Julien Masson <jmasson@baylibre.com>
Reviewed-by: Guillaume La Roque <glaroque@baylibre.com>
Tested-by: Guillaume La Roque <glaroque@baylibre.com>
Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

include/bootflow.h

@@ -408,6 +408,15 @@ void bootflow_remove(struct bootflow *bflow);
  */
 int bootflow_iter_check_blk(const struct bootflow_iter *iter);
 
+/**
+ * bootflow_iter_check_mmc() - Check that a bootflow uses a MMC device
+ *
+ * This checks the bootdev in the bootflow to make sure it uses a mmc device
+ *
+ * Return: 0 if OK, -ENOTSUPP if some other device is used (e.g. ethernet)
+ */
+int bootflow_iter_check_mmc(const struct bootflow_iter *iter);
+
 /**
  * bootflow_iter_check_sf() - Check that a bootflow uses SPI FLASH
  *