USB: fsl_qe_udc: send ZLP when zero flag and length % maxpacket == 0

The driver did not take the zero flag in the USB request. If the
request length is the same as the endpoint's maxpacket, an additional
ZLP with no data has to be transmitted.

The method used here is inspired to what is done in fsl_udc_core.c
(and pxa27x_udc.c and at91_udc.c) where this is supported.

There already was a discussion about this topic with people from
Keymile, and I propose here a better implementation:

http://thread.gmane.org/gmane.linux.usb.general/38951

Signed-off-by: Valentin Longchamp <valentin.longchamp@keymile.com>
Acked-by: Li Yang <leoli@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>