mmc: SDHI should depend on SUPERH || ARCH_SHMOBILE

Fix build breakage on platforms, not providing readsw and writesw
functions, e.g., on x86(_64).

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Chris Ball <cjb@laptop.org>

drivers/mmc/host/Kconfig

diff --git a/drivers/mmc/host/Kconfig b/drivers/mmc/host/Kconfig
index 0b03cee..94df405 100644
--- a/drivers/mmc/host/Kconfig
+++ b/drivers/mmc/host/Kconfig
@@ -452,6 +452,7 @@
 
 config MMC_SDHI
 	tristate "SH-Mobile SDHI SD/SDIO controller support"
+	depends on SUPERH || ARCH_SHMOBILE
 	select MMC_TMIO_CORE
 	help
 	  This provides support for the SDHI SD/SDIO controller found in