dt-bindings: net: stm32-dwmac: Make each example a separate entry

Each independent example should be a separate entry. This allows for
'interrupts' to have different cell sizes.

The first example also has a phandle in 'interrupts', so drop the phandle.

Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220106182518.1435497-8-robh@kernel.org