This driver exectue connecting the shared irq one time for
every status "okay" vcmp nodes, then it will show enable
the same irq multiple times when build.
So I check whether the irq is enabled or not, if yes,
we needn't to enable again. And we will figure out the
triggered channel in vcmp_it8xxx2_isr().
Signed-off-by: Ruibin Chang <Ruibin.Chang@ite.com.tw>