tests: drivers: Unit test for it82xx2_evb board

The below is the unit test result for the driver and kernel of
it82xx2_evb board.

GPIO/gpio_basic_api: PASS
I2C/i2c_api: PASS
Flash: PASS
UART/uart_basic_api: PASS
PWM/pwm_api: PASS
WDT/wdt_basic_api: PASS
KSCAN/kscan_api: PASS
kernel/sched/schedule_api: PASS
kernel/sched/preempt: PASS
kernel/timer/timer_api: PASS
kernel/sleep: PASS
ADC/adc_api: PASS.
ADC note: conversion time~=61.6us
          sample time delay~=60us
          wait voltage stable time~=202.8us
Set sampling time to 500us will pass for ADC test.

Signed-off-by: Tim Lin <tim2.lin@ite.corp-partner.google.com>