msm: ipa: create a general interface for the uC

This change creates a general interface for communicating with the uC,
similarly to the way commands are being sent to the IPA
(via send_cmd function).

Change-Id: I3cf221c8c90de43ea21069d886b2df11363054a0
Acked-by: David Arinzon <darinzon@qti.qualcomm.com>
Signed-off-by: Sivan Reinstein <sivanr@codeaurora.org>
Signed-off-by: Ravit Katzav <rkatzav@codeaurora.org>