dt-bindings: net: dsa: microchip: Make pinctrl 'reset' optional

dt-bindings: net: dsa: microchip: Make pinctrl 'reset' optional

Commit e469b87e0fb0d ("dt-bindings: net: dsa: microchip: Add strap
description to set SPI mode") required both 'default' and 'reset' pinctrl
states for all compatible devices. However, this requirement should be only
applicable to KSZ8463.

Make the 'reset' pinctrl state optional for all other Microchip DSA
devices while keeping it mandatory for KSZ8463.

Fix below CHECK_DTBS warnings:
  arch/arm64/boot/dts/freescale/imx8mp-skov-basic.dtb: switch@5f (microchip,ksz9893): pinctrl-names: ['default'] is too short
	from schema $id: http://devicetree.org/schemas/net/dsa/microchip,ksz.yaml#

Signed-off-by: Frank Li <Frank.Li@nxp.com>
Reviewed-by: Marco Felsch <m.felsch@pengutronix.de>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://patch.msgid.link/20260106143620.126212-1-Frank.Li@nxp.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>