common/octeontx2: add mailbox send and receive support

common/octeontx2: add mailbox send and receive support

Each RVU device has a dedicated 64KB mailbox region
shared with its peer for communication. RVU AF has
a separate mailbox region shared with each of RVU PFs
and an RVU PF has a separate region shared with each of
it's VF.

This patch add use 64KB memory and implemented mailbox
send and receive support.

These set of APIs are used by this driver (RVU AF) and
other RVU PF/VF drivers eg ethdev, cryptodev e.t.c.

Signed-off-by: Jerin Jacob <jerinj@marvell.com>
Signed-off-by: Vamsi Attunuru <vattunuru@marvell.com>
Signed-off-by: Nithin Dabilpuram <ndabilpuram@marvell.com>