MIPS: EVA: Add new EVA header

MIPS: EVA: Add new EVA header

Generic code may need to perform certain operations when EVA is
enabled, for example, configure the segmentation registers during
boot. In order to avoid using more CONFIG_EVA ifdefs in the arch code,
such functions will be added in this header instead.
Initially this header contains a macro which will be used by generic
code later on during VPEs configuration on secondary cores.
All it does is to call the platform specific EVA init code in case
EVA is enabled.

Reviewed-by: Paul Burton <paul.burton@imgtec.com>
Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Patchwork: http://patchwork.linux-mips.org/patch/7422/
Signed-off-by: James Hogan <james.hogan@imgtec.com>