can: grcan: Add device driver for GRCAN and GRHCAN cores

This driver supports GRCAN and CRHCAN CAN controllers available in the GRLIB
VHDL IP core library.

Signed-off-by: Andreas Larsson <andreas@gaisler.com>
Acked-by: Wolfgang Grandegger <wg@grandegger.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>