dfu: Provide means to find difference between dfu-util -e and -R

dfu: Provide means to find difference between dfu-util -e and -R

This commit provides distinction between DFU device detach and reset.
The -R behavior is preserved with proper handling of the dfu-util's -e
switch, which detach the DFU device.

By running dfu-util -e; one can force device to finish the execution of
dfu command on target and execute some other scripted commands.

Moreover, some naming has been changed - the dfu_reset() method now is known
as dfu_detach(). New name better reflects the purpose of the code.

It was also necessary to increase the number of usb_gadget_handle_interrupts()
calls since we also must wait for detection of the USB reset event.

Example usage:
1. -e (detach) switch
 dfu-util -a0 -D file1.bin;dfu-util -a3 -D uImage;dfu-util -e

 access to u-boot prompt.

2. -R (reset) switch
 dfu-util -a0 -D file1.bin;dfu-util -R -a3 -D uImage

 target board reset

Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>
Reviewed-by: Stephen Warren <swarren@nvidia.com>
Tested-by: Stephen Warren <swarren@nvidia.com>