platform/x86: intel_pmc_ipc: Drop intel_pmc_ipc_command()

Now that all callers have been converted over to the SCU IPC API we can
drop intel_pmc_ipc_command().

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>