platform/x86: intel_scu_ipc: Introduce new SCU IPC API

The current SCU IPC API has been operating on a single instance and
there has been no way to pin the providing module in place when the SCU
IPC is in use.

This implements a new API that takes the SCU IPC instance as first
parameter (NULL means the single instance is being used). The SCU IPC
instance can be retrieved by calling new function intel_scu_ipc_dev_get()
that take care of pinning the providing module in place as long as
intel_scu_ipc_dev_put() is not called.

The old API is updated to call the new API and is is left there in the
legacy API header to support the existing users that cannot be converted
easily.

Subsequent patches will convert most of the users over to the new API.

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>