genirq: Make early_irq_init() print out more informative

The printk in early_irq_init() is cryptic and badly formatted:

  NR_IRQS:33024 nr_irqs:968 16

The last number is the number of preallocated interrupts, so add a prefix
to it:

  NR_IRQS: 33024, nr_irqs: 968, preallocated irqs: 16

Cleanup the formatting for better readability as well.

Signed-off-by: Vincent Legoll <vincent.legoll@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/1494318849-6733-1-git-send-email-vincent.legoll@gmail.com