usb/gadget: fastboot: implement sparse format

- add capability to "fastboot flash" with sparse format images

Signed-off-by: Steve Rae <srae@broadcom.com>
Acked-by: Lukasz Majewski <l.majewski@samsung.com>
diff --git a/common/Makefile b/common/Makefile
index 443e54c..66c4f2f 100644
--- a/common/Makefile
+++ b/common/Makefile
@@ -266,6 +266,7 @@
 
 # This option is not just y/n - it can have a numeric value
 ifdef CONFIG_FASTBOOT_FLASH_MMC_DEV
+obj-y += aboot.o
 obj-y += fb_mmc.o
 endif