driver: adc: npcx: enable adding work queue for adc comparator

ADC comparator driver submits notifications into system work queue, this
change will make driver to use dedicated work queue instead by using
`CONFIG_ADC_CMP_NPCX_WORKQUEUE`.

Dedicated work queue and priority are configurable as well.

Signed-off-by: Bernardo Perez Priego <bernardo.perez.priego@intel.com>