ARM: keystone_defconfig: enable mdio and marvell eth phys

Enable MDIO support for Keystone 2 SoCs and also
enable Marvell Ethernet PHYs support for Keystone 2 K2H EVM
which has two 1G Marvell 88E1111-B2 PHYs installed.

For more information see:
- http://www.advantech.com/Support/TI-EVM/EVMK2HX.aspx



Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Santosh Shilimkar <ssantosh@kernel.org>