can: peak_canfd: provide hw timestamps in rx skbs

PEAK-System's CAN FD interfaces based on an IP core provide a timestamp
for each CAN and STATUS message received. This patch transfers these
received timestamps (clocked in microseconds) to hardware timestamps
(clocked in nanoseconds) in the corresponding skbs raised to the network
layer.

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