Replace infinite wait with a time-limited wait. In case a blocking
IDC message is not handled within IDC_TIMEOUT, return an error
instead of waiting. This allows to debug stuck core-to-core communication
easier.

Signed-off-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>

The IDC message objects are stored to static "idc_work", so
the cache operations are unnecessary when pointers to these
messages are passed around.

Signed-off-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>

A race exists between submitting a new IDC message and completion
of a previous message. The p4wq interface mandates k_p4wq_wait() must
be called to claim back ownership of the work object.  The SOF IDC
code does not do this, but relies on the caller not to send multiple
IDC messages to the same destination core.

Add appropriate calls to k_p4wq_wait() to handle this issue. If caller
wants to send an IDC in blocking mode, also call k_p4wq_wait() in
blocking mode. If non-blocking, return -EBUSY immediately.

The check for CPU status is moved earlier in the function. No pointing
in waiting for p4wq semaphore if the target core is already powered
down, so do the power state check as the first step.

Signed-off-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>