board: phytec: am64x: Add PHYTEC phyCORE-AM64x SoM

Add support for PHYTEC phyCORE-AM64x SoM.

Supported features:
  - 2GB DDR4 RAM
  - eMMC Flash
  - external uSD
  - OSPI NOR Flash
  - debug UART

Product page SoM: https://www.phytec.com/product/phycore-am64x



Device trees were taken from Linux v6.8-rc2.

Signed-off-by: Wadim Egorov <w.egorov@phytec.de>
Reviewed-by: Dhruva Gole <d-gole@ti.com>