can: m_can: add PCI glue driver for Intel Elkhart Lake

Add support for M_CAN controller on Intel Elkhart Lake attached to the PCI bus.
It integrates the Bosch M_CAN controller with Message RAM and the wrapper IP
block with additional registers which all of them are within the same MMIO
range.

Currently only interrupt control register from wrapper IP is used and the MRAM
configuration is expected to come from the firmware via "bosch,mram-cfg" device
property and parsed by m_can.c core.

Initial implementation is done by Felipe Balbi while he was working at Intel
with later changes from Raymond Tan and me.

Co-developed-by: Felipe Balbi (Intel) <balbi@kernel.org>
Co-developed-by: Raymond Tan <raymond.tan@intel.com>
Signed-off-by: Felipe Balbi (Intel) <balbi@kernel.org>
Signed-off-by: Raymond Tan <raymond.tan@intel.com>
Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Link: https://lore.kernel.org/r/20201117160827.3636264-1-jarkko.nikula@linux.intel.com
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>