mediatek: mt7623: set PREEMPT_NONE as default model

mediatek: mt7623: set PREEMPT_NONE as default model

Mediatek/mt7623 currently uses the PREEMPT model, which is not aligned with
OpenWrt's default. Switch to PREEMPT_NONE for consistency with OpenWrt's
default configuration. Preemption model selection is now available via
menuconfig for further customization.

Signed-off-by: Thomas Richard <thomas.richard@bootlin.com>
Link: https://github.com/openwrt/openwrt/pull/21413
[Added some config options again]
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>