arch: common: multilevel irq: fix issues where the intc device is NULL

The `irq` argument of the `Z_IF_DT_INTC_IRQN_EQ` macro
coincides with the `'irq'` argument passed into the `DT_IRQ`
macro, the former was supposed to be a number, while the latter
is a string/type, together this means that it was intepreted
as:

```c
DT_IRQ(node_id, <some_number>)
```

instead of

```c
DT_IRQ(node_id, irq)
```

as intended, so the macros never managed to match a device with
the IRQ properly, resulting in the `dev` member of the table
being NULL.

Solve this by renaming all the `irq` args in the macros to
`_irq` to avoid mixed usage.

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