ARM: msm: qcom: Replace NPU mailbox with AOP mailbox

NPU mailbox is not used by NPU driver currently. Replace it with
AOP mailbox in order to communicate with AOP for CDSP rate-matching
optimization.

Change-Id: I366bfd934c089630e31374779838485d4a507abf
Signed-off-by: Jilai Wang <jilaiw@codeaurora.org>