dfu: Implementation of target reset after communication with dfu-util's -R switch

This patch extends dfu code to support transmission with -R switch
specified at dfu-util.

When -R is specified, the extra USB_REQ_DFU_DETACH request is sent after
successful data transmission. Then dfu resources are released and reset
command is issued.

Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>