dts: Add a u-boot specific dtsi file for the am4372

This file is used to override the values found in am4372.dtsi
Use it to fix the "compatible" options for the controllers used
to support the USB (parent bus and syscons).

Signed-off-by: Jean-Jacques Hiblot <jjhiblot@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>