stm32mp1: add an IO to read MMC devices

Whereas the GPT table is read with io_block, the binaries to be loaded
(e.g. BL33) cannot use it, as it is not suitable to read them block by
block, or the boot time would be very bad.

Signed-off-by: Yann Gautier <yann.gautier@st.com>
diff --git a/include/drivers/st/io_mmc.h b/include/drivers/st/io_mmc.h
new file mode 100644
index 0000000..de71e7d
--- /dev/null
+++ b/include/drivers/st/io_mmc.h
@@ -0,0 +1,14 @@
+/*
+ * Copyright (c) 2015-2018, ARM Limited and Contributors. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#ifndef IO_MMC_H
+#define IO_MMC_H
+
+#include <io_driver.h>
+
+int register_io_dev_mmc(const io_dev_connector_t **dev_con);
+
+#endif /* IO_MMC_H */