soc/ite/it8xxx2: make ARCH_IRQ_VECTOR_TABLE_ALIGN constant

The IQR vector table changed size since a825e01 and it is
causing issues with downstream applications, for example,
data stored in bin specific field is shifted by
the ARCH_IRQ_VECTOR_TABLE_ALIGN, so I make
ARCH_IRQ_VECTOR_TABLE_ALIGN constant.

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