overlays: Overlays for WaveShare 2-Chan CAN FD HAT

This patch adds the overlays for the Waveshare 2-Channel Isolated
CAN FD Expansion HAT for Raspberry Pi, Multi Protections. This HAT
is based on the mcp2518fd chip and can be run in two modes

Mode A: can0 on spi0.0 and can1 on spi1.0 (cs = pin 26)
Mode B: can1 on spi0.0 and can1 in spi0.1

Interupts: can0 pin 25 / can1 pin 16

https://www.waveshare.com/2-ch-can-fd-hat.htm

Overlays generated by:
Mode A: ovmerge -c spi1-1cs-overlay.dts,cs0_pin=26,cs0_spidev=false \
              mcp251xfd-overlay.dts,spi0-0,interrupt=25 \
              mcp251xfd-overlay.dts,spi1-0,interrupt=16

Mode B: ovmerge -c mcp251xfd-overlay.dts,spi0-0,interrupt=25 \
              mcp251xfd-overlay.dts,spi0-1,interrupt=16