ipc: make APR driver a platform driver

Change APR driver to platform driver and add any child
device only after ADSP up notification is received.
The idea is to have machine driver as a child device
under APR, and add the platform device for machine
driver only after ADSP is up. This will help invoke
audio drivers waiting with deferred probe and eventually
should help sound card registers successfully.

Change-Id: Ib0c0f7ec1d7dd93a1b54a9a66260861223d55c67
Signed-off-by: Laxminath Kasam <lkasam@codeaurora.org>
Signed-off-by: Meng Wang <mwang@codeaurora.org>
Signed-off-by: Banajit Goswami <bgoswami@codeaurora.org>