Currently the PMU driver is using DT based lookup to
find the INTC node for sscofpmf extension. This will not work
for ACPI based systems causing the driver to fail to register
the PMU overflow interrupt handler.

Hence, change the code to use the standard interface to find
the INTC node which works irrespective of DT or ACPI.
Signed-off-by: Sunil V L <sunilvl@ventanamicro.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
Link: https://lore.kernel.org/r/20230607112417.782085-3-sunilvl@ventanamicro.comSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>