USB: pxa27x_udc: compatibility with pxa320 SoC

Got pxa27x_udc working on the pxa320 Nomad platform.  The
problem was that the pxa3xx UDC is not quite compatible with
the pxa27x UDC in how it handles back-to-back control
packets.  The pxa27x probably drops them by default, but the
pxa320 does not, and you have to detect it and set the OPC
bit to clear the zero-length packet.

Signed-off-by: Aric Blumer <aric@sdgsystems.com>
Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>