RISC-V: smpboot: Add ACPI support in setup_smp()

Enable SMP boot on ACPI based platforms by using the RINTC
structures in the MADT table.

Signed-off-by: Sunil V L <sunilvl@ventanamicro.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>