contrib: add script to dump irq stats.

Sample output:

python3 -m drgn -s vmlinux -c vmcore contrib/irq.py

List of IRQs
irq: 0 name: timer (struct irq_desc *)0xffff9b42fd00d400  (struct irqaction *)0xffffffff88425240
irq: 1 name: i8042 (struct irq_desc *)0xffff9b42fd00d600  (struct irqaction *)0xffff9b42fcb13c00
irq: 4 name: ttyS0 (struct irq_desc *)0xffff9b42fd00dc00  (struct irqaction *)0xffff9b42fcb2bc00
irq: 8 name: rtc0 (struct irq_desc *)0xffff9b42fd00e400  (struct irqaction *)0xffff9b42fcb59380
irq: 9 name: acpi (struct irq_desc *)0xffff9b42fd00e600  (struct irqaction *)0xffff9b42fcafca80
irq: 11 name: eth0 (struct irq_desc *)0xffff9b42fd00ea00  (struct irqaction *)0xffff9b42fc878d80
irq: 12 name: i8042 (struct irq_desc *)0xffff9b42fd00ec00  (struct irqaction *)0xffff9b42fcb13900
irq: 14 name: ata_piix (struct irq_desc *)0xffff9b42fd00f000  (struct irqaction *)0xffff9b42fc690800
irq: 15 name: ata_piix (struct irq_desc *)0xffff9b42fd00f200  (struct irqaction *)0xffff9b42fc690780

IRQ affinities
irq: 0 name: timer affinity: 0-7
irq: 1 name: i8042 affinity: 0-7
irq: 4 name: ttyS0 affinity: 0-7
irq: 8 name: rtc0 affinity: 0-7
irq: 9 name: acpi affinity: 0-7
irq: 11 name: eth0 affinity: 0-7
irq: 12 name: i8042 affinity: 0-7
irq: 14 name: ata_piix affinity: 0-7
irq: 15 name: ata_piix affinity: 0-7

IRQ stats
irq: 0 name: timer (struct irq_desc *)0xffff9b42fd00d400
    CPU: 0  	 count: 162
    Total: 162
irq: 1 name: i8042 (struct irq_desc *)0xffff9b42fd00d600
    CPU: 0  	 count: 10
    Total: 10
irq: 4 name: ttyS0 (struct irq_desc *)0xffff9b42fd00dc00
    CPU: 0  	 count: 220
    Total: 220
irq: 8 name: rtc0 (struct irq_desc *)0xffff9b42fd00e400
    CPU: 0  	 count: 1
    Total: 1
    Total: 0
irq: 11 name: eth0 (struct irq_desc *)0xffff9b42fd00ea00
    CPU: 0  	 count: 85
    Total: 85
irq: 12 name: i8042 (struct irq_desc *)0xffff9b42fd00ec00
    CPU: 0  	 count: 125
    Total: 125
irq: 14 name: ata_piix (struct irq_desc *)0xffff9b42fd00f000
    CPU: 0  	 count: 496
    Total: 496
irq: 15 name: ata_piix (struct irq_desc *)0xffff9b42fd00f200
    CPU: 0  	 count: 11
    Total: 11

cpuwise IRQ stats
IRQ stats for cpu: 0
    irq: 0 name: timer (struct irq_desc *)0xffff9b42fd00d400 count: 162
    irq: 1 name: i8042 (struct irq_desc *)0xffff9b42fd00d600 count: 10
    irq: 4 name: ttyS0 (struct irq_desc *)0xffff9b42fd00dc00 count: 220
    irq: 8 name: rtc0 (struct irq_desc *)0xffff9b42fd00e400 count: 1
    irq: 11 name: eth0 (struct irq_desc *)0xffff9b42fd00ea00 count: 85
    irq: 12 name: i8042 (struct irq_desc *)0xffff9b42fd00ec00 count: 125
    irq: 14 name: ata_piix (struct irq_desc *)0xffff9b42fd00f000 count: 496
    irq: 15 name: ata_piix (struct irq_desc *)0xffff9b42fd00f200 count: 11
Total: 1110

IRQ stats for cpu: 1
Total: 0

IRQ stats for cpu: 2
Total: 0

IRQ stats for cpu: 3
Total: 0

IRQ stats for cpu: 4
Total: 0

IRQ stats for cpu: 5
Total: 0

IRQ stats for cpu: 6
Total: 0

IRQ stats for cpu: 7
Total: 0

Signed-off-by: Imran Khan <imran.f.khan@oracle.com>