dt-binding: net: ti: am65x-cpts: make reg and compatible required

This patch follows K3 CPTS review comments from Rob Herring
<robh@kernel.org>.
 - "reg" and "compatible" properties are required now
 - minor format changes
 - K3 CPTS example added to K3 MCU CPSW bindings

Cc: Rob Herring <robh@kernel.org>
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>