RISC-V/perf: Use standard interface to get INTC domain

As part of "RISC-V IPI Improvements" patch series, there is a
new interface for drivers to use to discover the INTC hwnode.

This patch is required to support SSCOFPMF irrespective of
DT or ACPI.

Signed-off-by: Sunil V L <sunilvl@ventanamicro.com>