tests: devicetree: api: add tests for new DT APIs

Add tests for new DT APIs added in the previous commit:
- `DT_IRQN_BY_IDX`
- `DT_INST_IRQN_BY_IDX`

Added additional tests for the following existing DT APIs when
`CONFIG_MULTI_LEVEL_INTERRUPTS` is enabled:
- `DT_IRQN`
- `DT_INST_IRQN`

Added `qemu_riscv32` for the multi-level interrupt tests.

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