octeontx2-af: Add new mbox to support multicast/mirror offload

commit cf0e3c68e7abe94f37624a3083a71743e55304ca from
git@git.assembla.com:cavium/WindRiver.linux.git

A new mailbox is added to support offloading of multicast/mirror
functionality. The mailbox also supports dynamic updation of the
multicast/mirror list.

Signed-off-by: Suman Ghosh <sumang@marvell.com>
Change-Id: I18bf759026e5a41de58a13e94c82f370f7d47086
Reviewed-on: https://sj1git1.cavium.com/c/IP/SW/kernel/linux/+/114739


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>