octeontx2-af: extend context reading capability

commit bf64a4030cc35fd0fe798e5569bdf9107d566959 from
git@git.assembla.com:cavium/WindRiver.linux.git

Exporting the mbox handler used to read the SQ/RQ/CQ/AURA/POOL
context. This is used to honor context reading request made by
user via hw access driver.

Change-Id: I40d5a3022ee23ff0c9511d48f6dd7d2088d3a6d2
Signed-off-by: Harman Kalra <hkalra@marvell.com>
Reviewed-on: https://sj1git1.cavium.com/c/IP/SW/kernel/linux/+/55861
Tested-by: sa_ip-sw-jenkins <sa_ip-sw-jenkins@marvell.com>
Reviewed-by: Sunil Kovvuri Goutham <sgoutham@marvell.com>
Signed-off-by: Ruiqiang Hao <Ruiqiang.Hao@windriver.com>