dt-bindings: net: dsa: microchip: Add strap description to set SPI mode

dt-bindings: net: dsa: microchip: Add strap description to set SPI mode

At reset, KSZ8463 uses a strap-based configuration to set SPI as
interface bus. If the required pull-ups/pull-downs are missing (by
mistake or by design to save power) the pins may float and the
configuration can go wrong preventing any communication with the switch.

Add a 'reset' pinmux state
Add a KSZ8463 specific strap description that can be used by the driver
to drive the strap pins during reset. Two GPIOs are used. Users must
describe either both of them or none of them.

Signed-off-by: Bastien Curutchet (Schneider Electric) <bastien.curutchet@bootlin.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://patch.msgid.link/20250918-ksz-strap-pins-v3-2-16662e881728@bootlin.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>