mmc: move MMC_SDHCI_IO_ACCESSORS to Kconfig

This is a user-unconfigurable option that is selected by the
drivers that need to overwrite SDHCI IO memory accessors.
(BCM2835 SDHCI seems the only driver that needs to do so.)

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>
diff --git a/drivers/mmc/Kconfig b/drivers/mmc/Kconfig
index cfb4e14..2ba1254 100644
--- a/drivers/mmc/Kconfig
+++ b/drivers/mmc/Kconfig
@@ -132,6 +132,13 @@
 
 	  If unsure, say N.
 
+config MMC_SDHCI_IO_ACCESSORS
+	bool
+	depends on MMC_SDHCI
+	help
+	  This is silent Kconfig symbol that is selected by the drivers that
+	  need to overwrite SDHCI IO memory accessors.
+
 config MMC_SDHCI_SDMA
 	bool "Support SDHCI SDMA"
 	depends on MMC_SDHCI
@@ -143,6 +150,7 @@
 	tristate "SDHCI support for the BCM2835 SD/MMC Controller"
 	depends on ARCH_BCM283X
 	depends on MMC_SDHCI
+	select MMC_SDHCI_IO_ACCESSORS
 	help
 	  This selects the BCM2835 SD/MMC controller.