dfu: add backend for MTD device

Add DFU backend for MTD device: allow to read
and write on all MTD device (NAND, SPI-NOR,
SPI-NAND,...)

For example :
> set dfu_alt_info "nand_raw raw 0x0 0x100000"
> dfu 0 mtd nand0

This MTD backend provides the same level than dfu nand
backend for NAND and dfu sf backend for SPI-NOR;
So it can replace booth of them but it also
add support of spi-nand.

> set dfu_alt_info "nand_raw raw 0x0 0x100000"
> dfu 0 mtd spi-nand0

The backend code is based on the "mtd" command
introduced by commit 5db66b3aee6f ("cmd: mtd:
add 'mtd' command")

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
diff --git a/include/dfu.h b/include/dfu.h
index 7d60ffc..924952f 100644
--- a/include/dfu.h
+++ b/include/dfu.h
@@ -22,6 +22,7 @@
 	DFU_DEV_NAND,
 	DFU_DEV_RAM,
 	DFU_DEV_SF,
+	DFU_DEV_MTD,
 };
 
 enum dfu_layout {
@@ -55,6 +56,14 @@
 	unsigned int part;
 };
 
+struct mtd_internal_data {
+	struct mtd_info *info;
+
+	/* RAW programming */
+	u64 start;
+	u64 size;
+};
+
 struct nand_internal_data {
 	/* RAW programming */
 	u64 start;
@@ -105,6 +114,7 @@
 
 	union {
 		struct mmc_internal_data mmc;
+		struct mtd_internal_data mtd;
 		struct nand_internal_data nand;
 		struct ram_internal_data ram;
 		struct sf_internal_data sf;
@@ -249,6 +259,17 @@
 }
 #endif
 
+#if CONFIG_IS_ENABLED(DFU_MTD)
+int dfu_fill_entity_mtd(struct dfu_entity *dfu, char *devstr, char *s);
+#else
+static inline int dfu_fill_entity_mtd(struct dfu_entity *dfu, char *devstr,
+				      char *s)
+{
+	puts("MTD support not available!\n");
+	return -1;
+}
+#endif
+
 /**
  * dfu_tftp_write - Write TFTP data to DFU medium
  *