riscv: dts: microchip: add the Aldec TySoM's devicetree

The TySOM-M-MPFS250 is a compact SoC prototyping board featuring
a Microchip PolarFire SoC MPFS250T-FCG1152. Features include:
- 16 Gib FPGA DDR4
- 16 Gib MSS DDR4 with ECC
- eMMC
- SPI flash memory
- 2x Ethernet 10/100/1000
- USB 2.0
- PCIe x4 Gen2
- HDMI OUT
- 2x FMC connector (HPC and LPC)

Specifically flag this board as rev2, in case later boards have an
FPGA design revision with more features available in the future.

Link: https://www.aldec.com/en/products/emulation/tysom_boards/polarfire_microchip/tysom_m_mpfs250


[Fixed a mistake where I read 16 Gib as 16 GiB!]
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>