spmi: pmic_arb: add support for interrupt handling
The Qualcomm PMIC Arbiter, in addition to being a basic SPMI controller,
also implements interrupt handling for slave devices. Note, this is
outside the scope of SPMI, as SPMI leaves interrupt handling completely
unspecified.
Extend the driver to provide a irq_chip implementation and chained irq
handling which allows for these interrupts to be used.