arm64: dts: renesas: spider-ethernet: Access rswitch ports via phandles

arm64: dts: renesas: spider-ethernet: Access rswitch ports via phandles

The r8a779f0.dtsi now contains labels for each rswitch port in the form
'rswitch_portN'.  Use those to access rswitch ports and slightly reduce
the depth of this board DT.  No functional change.

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/20250118111344.361617-2-marek.vasut+renesas@mailbox.org
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>