All Atmel-provided CMSIS-DAP devices use 512 byte packet size

All Atmel-provided CMSIS-DAP devices use 512 byte packet size

The existing CMSIS-DAP driver matches the USB VID/PID against 0x3eb
(Atmel VID) and 0x2111 (Atmel EDBG embedded CMSIS-DAP debugger), and
then bumps the packet size from its default of 64 to 512.  However, it
turned out that *all* Atmel-provided CMSIS-DAP devices (EDBG with PID
0x2111; JTAGICE3 with firmware version 3.x, PID 0x2140; new Atmel-ICE
[successor of JTAGICE3], PID 0x2141) require a 512-byte packet size.
Obviously, all run the same USB implementation inside their custom
microcontroller.  Thus, it seems best to simply assume that *all*
Atmel CMSIS-DAP devices use this packet size, and don't check the PID
at all.

This has also been filed as Trac bug #68:

https://sourceforge.net/apps/trac/openocd/ticket/68

Change-Id: I942af93060fdf265fca3961841638caa6182f877
Signed-off-by: Jörg Wunsch <openocd@uriah.heep.sax.de>
Reviewed-on: http://openocd.zylin.com/2045
Tested-by: jenkins
Reviewed-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-by: Andrey Yurovsky <yurovsky@gmail.com>