platform/x86: intel_scu_ipc: Fix interrupt support

Currently the driver has disabled interrupt support for Tangier but
actually interrupt works just fine if the command is not written twice
in a row. Also we need to ack the interrupt in the handler.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>