mtd: install header files to staging directory

These header files are required by swupdate.

Signed-off-by: Jörg Krause <joerg.krause@embedded.rocks>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/mtd/mtd.mk

@@ -107,6 +107,9 @@ endef
 define MTD_INSTALL_STAGING_CMDS
 	$(INSTALL) -D -m 0755 $(@D)/lib/libmtd.a $(STAGING_DIR)/usr/lib/libmtd.a
 	$(INSTALL) -D -m 0755 $(@D)/ubi-utils/libubi.a $(STAGING_DIR)/usr/lib/libubi.a
+	$(INSTALL) -D -m 0644 $(@D)/include/libmtd.h $(STAGING_DIR)/usr/include/mtd/libmtd.h
+	$(INSTALL) -D -m 0644 $(@D)/ubi-utils/include/libubi.h $(STAGING_DIR)/usr/include/mtd/libubi.h
+	$(INSTALL) -D -m 0644 $(@D)/include/mtd/ubi-media.h $(STAGING_DIR)/usr/include/mtd/ubi-media.h
 endef
 
 define MTD_INSTALL_TARGET_CMDS