platform: Add firmware-agnostic irq and affinity retrieval interface

platform: Add firmware-agnostic irq and affinity retrieval interface

Expand platform_get_irq_optional() to also return an affinity if available,
renaming it to platform_get_irq_affinity() in the process.

platform_get_irq_optional() is preserved with its current semantics by
calling into the new helper with a NULL affinity pointer.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Will Deacon <will@kernel.org>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Link: https://patch.msgid.link/20251020122944.3074811-5-maz@kernel.org