dfu: DFU backend implementation

New, separate driver at ./drivers/dfu has been added. It allows platform
and storage independent operation of DFU.
It has been extended to use new MMC level of command abstraction.

Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Marek Vasut <marex@denx.de>
diff --git a/Makefile b/Makefile
index a41b987..cc15bfd 100644
--- a/Makefile
+++ b/Makefile
@@ -269,6 +269,7 @@
 LIBS-y += drivers/pcmcia/libpcmcia.o
 LIBS-y += drivers/power/libpower.o
 LIBS-y += drivers/spi/libspi.o
+LIBS-y += drivers/dfu/libdfu.o
 ifeq ($(CPU),mpc83xx)
 LIBS-y += drivers/qe/libqe.o
 LIBS-y += arch/powerpc/cpu/mpc8xxx/ddr/libddr.o