arm: rmobile: Add missed header file for Silk board

This file was missed in the commit
https://patchwork.ozlabs.org/patch/427801/

Signed-off-by: Vladimir Barinov <vladimir.barinov@cogentembedded.com>
Signed-off-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
1 file changed