platform/x86: intel_pmc_ipc: Start using SCU IPC

SCU IPC is pretty much the same IPC implemented in the intel_pmc_ipc
driver so drop the duplicate implementation and call directly the SCU
IPC.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>