can: peak_usb: export pcan_usb_pro functions

Add support for the following new PEAK-System technik CANFD USB adapters:

PCAN-USB FD             single CANFD channel USB adapter
PCAN-USB Pro FD         dual CANFD channels USB adapter

The communication protocol has been developed using some mechanisms that
did exist in the PCAN-USB Pro, thus, this patch also changes some
previously static functions and data into global ones.

Signed-off-by: Stephane Grosjean <s.grosjean@peak-system.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>