driver: adc: an adc driver for rt1170

reuse the lpc's lpadc driver for rt1170, modify the dts and add
some macro to shield some code of LPC series. Also add the
board support inside the tests/drivers/adc/adc_api/src/test_adc.c,
and a dts node:zephyr,user inside
samples/drivers/adc/boards/mimxrt1170_evk_cm7.overlay

Signed-off-by: Crist Xu <crist.xu@nxp.com>