scripts: dts: gen_defines: Generate interrupt-controller macro

Extend the gen_defines.py write_interrupts(node) function to
generate macros to get the interrupt controller for an
interrupt specifier by idx and by name.

The information is already generated by edtlib.py and stored in
node.interrupts[].controller. This addition uses the node pointed
to by the controller member to generate the following example output

define DT_N_S_device1_IRQ_IDX_0_CONTROLLER \
       DT_N_S_gpio_800

define DT_N_S_device1_IRQ_NAME_test4_CONTROLLER \
       N_S_device1_IRQ_IDX_0_CONTROLLER

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