soc arm: MEC172x soc.h - Include custom IRQn_Type

Fix for issue #41012 to allow compiler to treat
IRQn_Type to be more than 8-bit. This will ensure NVIC numbers
more than 127 (required for MEC172x device) will work
correctly with irq_enable() API

Signed-off-by: Jay Vasanth <jay.vasanth@microchip.com>