A_IRQ: sadf: Update PCP interface for interrupts statistics

A_IRQ: sadf: Update PCP interface for interrupts statistics

Update/create new PCP metrics for interrupts statistics:

kernel.all.intr: This is the total number of all interrupts among
all processors

kernel.all.interrupts.total: This is the total number of each interrupt
among all processors. A domain instance is created for each interrupt
("0", "1", "LOC", "CAL", etc.)

kernel.percpu.interrupts.XXX: This is the number of interrupts XXX for a
given processor. A domain instance is created for each processor (cpu0,
cpu1, etc.)
E.g.:
kernel.percpu.interrupts.sum is the total number of all interrupts for a
given processor.
kernel.percpu.interrupts.LOC is the number of LOC interrupts for a given
processor.
Metric names cannot contain digits. As a consequence,
kernel.percpu.interrupts.0 is replaced with kernel.percpu.interrupts.a
kernel.percpu.interrupts.1 is replaced with kernel.percpu.interrupts.b
kernel.percpu.interrupts.30 is replaced with kernel.percpu.interrupts.da
etc.

Signed-off-by: Sebastien GODARD <sysstat@users.noreply.github.com>