gen_isr_tables: print index number at the end of each entry as comment
Make it easier to debug by printing the index number at the
end, this is especially helpful when there's a lot of
interrupts.
Before:
```c
/* build/zephyr/isr_tables.c */
{(const void *)0x0, (ISR)((uintptr_t)&z_irq_spurious)},
{(const void *)0x0, (ISR)((uintptr_t)&z_irq_spurious)},
{(const void *)0x0, (ISR)((uintptr_t)&z_irq_spurious)},
{(const void *)0x0, (ISR)((uintptr_t)&z_irq_spurious)},
{(const void *)0x0, (ISR)((uintptr_t)&z_irq_spurious)},
{(const void *)0x0, (ISR)((uintptr_t)&z_irq_spurious)},
{(const void *)0x0, (ISR)((uintptr_t)&z_irq_spurious)},
```
After:
```c
/* build/zephyr/isr_tables.c */
{(const void *)0x0, (ISR)((uintptr_t)&z_irq_spurious)}, /* 0 */
{(const void *)0x0, (ISR)((uintptr_t)&z_irq_spurious)}, /* 1 */
{(const void *)0x0, (ISR)((uintptr_t)&z_irq_spurious)}, /* 2 */
{(const void *)0x0, (ISR)((uintptr_t)&z_irq_spurious)}, /* 3 */
{(const void *)0x0, (ISR)((uintptr_t)&z_irq_spurious)}, /* 4 */
{(const void *)0x0, (ISR)((uintptr_t)&z_irq_spurious)}, /* 5 */
{(const void *)0x0, (ISR)((uintptr_t)&z_irq_spurious)}, /* 6 */
```
Signed-off-by: Yong Cong Sin <ycsin@meta.com>
89fb8f8b98