ARM: dts: ti: Add AM57xx GP EVM Rev A3 board support

The A3 revision of the AM57xx GP EVM has the same EVM feature set as the
original but is paired with an updated revision C BeagleBoard X15.

DT Overlays allow us to model this in the same way, we simply apply the
EVM overlay to the Rev C BeagleBoard to create the Rev A3 AM57xx GP EVM.

Signed-off-by: Andrew Davis <afd@ti.com>
Message-Id: <20230307161715.15209-3-afd@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>