dt-bindings: net: dsa: microchip: Group if clause under allOf tag

Upcoming patch adds a new if/then clause. It requires to be grouped with
the already existing if/then clause under an 'allOf:' tag.

Move the if/then clause under the already existing 'allOf:' tag to
prepare next patch.

Acked-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Bastien Curutchet (Schneider Electric) <bastien.curutchet@bootlin.com>
Link: https://patch.msgid.link/20250918-ksz-strap-pins-v3-1-16662e881728@bootlin.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>