spmi-pmic-arb: check apid enabled before calling the handler

The driver currently invokes the apid handler (periph_handler()) once it
sees that the summary status bit for that apid is set.

However the hardware is designed to set that bit even if the apid
interrupts are disabled. The driver should check whether the apid is
indeed enabled before calling the apid handler.

CRs-Fixed: 1001770
Change-Id: I1415c41ec99ca4b767392ea3443691760f967953
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>