arm: rmobile: silk: Add support SDHI

This adds GPIO configuration and initialization function of SDHI on Silk board

Signed-off-by: Vladimir Barinov <vladimir.barinov+renesas@cogentembedded.com>
Signed-off-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
diff --git a/configs/silk_defconfig b/configs/silk_defconfig
index 3130e93..23d4f58 100644
--- a/configs/silk_defconfig
+++ b/configs/silk_defconfig
@@ -3,3 +3,4 @@
 CONFIG_TARGET_SILK=y
 CONFIG_DM=y
 CONFIG_DM_SERIAL=y
+CONFIG_SH_SDHI=y