spmi: pmic-arb: Don't disable arbiter interrupt when no clients use it

The GIC interrupt should not be firing when the arbiter interrupts
(peripheral interrupts) are disabled. So enabling/disabling the GIC
interrupt is not necessary. Remove those calls, and corresponding
reference counter logic.

Change-Id: Ice8d76ef255ec6c154c546dbd17807012558fe84
Signed-off-by: Gilad Avidov <gavidov@codeaurora.org>
Signed-off-by: David Brown <davidb@codeaurora.org>