ARM: configs: keystone: Enable Message Manager

Message Manager is a communication hardware block on 66AK2G[1] SoCs.
Enable the same to provide support for communication with 66AK2G Power
Management Micro Controller (PMMC) via the TISCI protocol[2].

[1] http://www.ti.com/product/66ak2g02
[2] http://processors.wiki.ti.com/index.php/TISCI



Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Santosh Shilimkar <ssantosh@kernel.org>