ITE drivers/kscan: clean up it8xxx2 kscan driver

1.Declare the member type to match the kscan_it8xxx2_regs, so
we needn't to transform the local structure in the function.
2.Stop using DRV_CONFIG, DRV_DATA, DRV_REG macros.
3.Delete unused register defines.

Signed-off-by: Ruibin Chang <Ruibin.Chang@ite.com.tw>