can: usb: PEAK-System Technik USB adapters driver core

This patch adds the core of the peak_usb driver which handles PEAK-System
Technik PCAN USB adapters. It defines the parts which are common to the
PCAN-USB adapters: can network interfaces management, network-to/from-usb
data path interface, timestamps management...

Tested-by: Oliver Hartkopp <socketcan@hartkopp.net>
Acked-by: Wolfgang Grandegger <wg@grandegger.com>
Signed-off-by: Stephane Grosjean <s.grosjean@peak-system.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>