bcm63xx: periph_intc: report effective affinity

bcm63xx: periph_intc: report effective affinity

The bcm6345-periph-intc driver only targets a single CPU at a time, even
if the notional affinity is wider. Let's inform the core code about this.

This patch gets rid of the kernel message:
"genirq: irq_chip bcm6345-periph-intc did not update eff. affinity mask
of irq 52"

Signed-off-by: Daniel Gonzalez Cabanelas <dgcbueu@gmail.com>
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
(cherry picked from commit e04ff3c7cc52c23f5b40730ee426710e22940d68)