platform: adsp:replace receive thread with handler

platform: adsp:replace receive thread with handler

The app_receive_thread waits on infinitely for receiving a mailbox
event. This can be made efficient by using a mailbox handler which
is called when a mailbox event/interrupt occurs.

Bug 1561453

Change-Id: I99d50d5a0e948a24494c18a906f3db45cbeedf21
Signed-off-by: Ajay Nandakumar <anandakumarm@nvidia.com>
Reviewed-on: http://git-master/r/553755
Reviewed-by: Automatic_Commit_Validation_User
GVS: Gerrit_Virtual_Submit
Reviewed-by: Nitin Kumbhar <nkumbhar@nvidia.com>