dt-bindings: serial: Convert cirrus,ep7209-uart to DT schema

dt-bindings: serial: Convert cirrus,ep7209-uart to DT schema

Convert the Cirrus EP7209 UART binding to DT schema. There is no user of
"cirrus,ep7312-uart" other than the example, so drop it. Drop the
"aliases" node part as it is not relevant to the schema. The modem
control GPIOs are covered by the serial.yaml schema and don't have to be
listed in the schema.

Signed-off-by: "Rob Herring (Arm)" <robh@kernel.org>
Reviewed-by: Thierry Reding <treding@nvidia.com>
Link: https://lore.kernel.org/r/20250506220021.2545820-1-robh@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>