msm: ipa: enable power collapse on AOP

Add mailbox struct for the IPA HW dtsi entry.
Add a function to construct and send a QMP message to enable
power collapse on AOP using this mailbox.

Change-Id: Ib67e6c5c1d93eda684c3e2114e4e840509486ab5
Signed-off-by: Michael Adisumarta <madisuma@codeaurora.org>