devicetree: add `DT_INST_NUM_IRQS()`

Add `DT_INST_NUM_IRQS()` to get the number of interrupt lines
of the current `DT_DRV_COMPAT`

Signed-off-by: Yong Cong Sin <ycsin@meta.com>
Signed-off-by: Yong Cong Sin <yongcong.sin@gmail.com>