Add initial CTU-CAN-FD core support.

[enjoy-digital]

Add CTU-CAN-FD core support: https://gitlab.fel.cvut.cz/canbus/ctucanfd_ip_core with:

• LiteX wrapper around it.
• litex_json2dts support.

Tested with simple SN65HVD230 transceivers on PMOD on:

• Arty A7 with VexRiscv-SMP + Linux + CTU-CAN-FD Linux driver + cantools.
• Arty Z7 with Zynq7000 + Linux + CTU-CAN-FD Linux driver + cantools.

Communication has been tested when connected to a USB <-> CAN cable but also for dump of CAN frames on a Tesla Model 3.

Integration example on Arty:

# Import Core.
from litex.build.generic_platform import *
from litex.soc.cores.can.ctu_can_fd import CTUCANFD

[...]

# Define CAN IOs on PMOD.
_ios = [
    ("can", 0,
        Subsignal("tx",  Pins("pmodc:2")),
        Subsignal("rx",  Pins("pmodc:3")),
        IOStandard("LVCMOS33"),
    ),
    ("can", 1,
        Subsignal("tx",  Pins("pmodb:2")),
        Subsignal("rx",  Pins("pmodb:3")),
        IOStandard("LVCMOS33"),
    ),
]

[...]

# CAN Core Instance.
can0 = CTUCANFD(platform, platform.request("can", 0))
self.add_module("can0", can0)
self.bus.add_slave("can0", can0.bus, SoCRegion(origin=0xb0010000, size=0x10000, mode="rw", cached=False))
self.irq.add("can0")

[AndrewD]

Fantastic, thanks @enjoy-digital !

[disdi]

Thanks @enjoy-digital for taking this in.