arm: rmobile: alt: Add support SDHI

Alt board has two SDHI port.
This adds GPIO configuration and initialization function of SDHI, and
enables MMC command.

Signed-off-by: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@renesas.com>
Signed-off-by: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
diff --git a/configs/alt_defconfig b/configs/alt_defconfig
index 8a6a0d3..ff87230 100644
--- a/configs/alt_defconfig
+++ b/configs/alt_defconfig
@@ -3,3 +3,4 @@
 CONFIG_TARGET_ALT=y
 CONFIG_DM=y
 CONFIG_DM_SERIAL=y
+CONFIG_SH_SDHI=y