arm: dts: k3-am642: Add initial support for EVM

The AM642 EValuation Module (EVM) is a board that provides access to
various peripherals available on the AM642 SoC, such as PCIe, USB 2.0,
CPSW Ethernet, ADC, and more.

Add basic support.

Signed-off-by: Dave Gerlach <d-gerlach@ti.com>