tests: lib: devicetree: api: Add tests for IRQ_INTC_* macros

Extend api test suite to cover the new devicetree macros. This
includes extending the devicetree overlay with two new bindings:

- GPIO device which is also an interrupt controller
- interrupt holder using interrupts-extended to point to both
  existing interrupt controller test_intc, and the newly added
  GPIO device

Signed-off-by: Bjarki Arge Andreasen <bjarki@arge-andreasen.me>