ipc: apr: add qcom,subsys-name for apr

Add qcom,subsys-name for apr driver. Based on the property,
registration of notifier is done for the right co-processor,
from which notification needs to be received.

Change-Id: Id492c8b24d1a4cf0bcab37700a1e9c61c9067041
Signed-off-by: Meng Wang <mengw@codeaurora.org>