habanalabs/gaudi2: add device unavailable notification

Device unavailable notifies the user that there isn't an option to
retrieve debug information from the device.
When a critical device error occurs and the f/w performs the device
reset, a device unavailable notification shall be sent to the user
process.

Signed-off-by: Tal Cohen <talcohen@habana.ai>
Reviewed-by: Oded Gabbay <ogabbay@kernel.org>
Signed-off-by: Oded Gabbay <ogabbay@kernel.org>