mfd: ab8500-debug: Add wake-up info

Add information regarding what ab interrupt that caused
a wake-up from suspend in <debugfs>/ab8500/interrupts.
Also print the name of the interrupts, not just the numbers.

Signed-off-by: Jonas Aaberg <jonas.aberg@stericsson.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Reviewed-by: Per FORLIN <per.forlin@stericsson.com>
Tested-by: Mattias WALLIN <mattias.wallin@stericsson.com>
Acked-by: Samuel Ortiz <sameo@linux.intel.com>