irqchip/riscv-intc: Add ACPI support

Add support for initializing the RISC-V INTC driver on ACPI
platforms.

Signed-off-by: Sunil V L <sunilvl@ventanamicro.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230515054928.2079268-17-sunilvl@ventanamicro.com


Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>