mfd: Add syscon driver based on regmap

Add regmap based syscon driver.
This is usually used for access misc bits in registers which does not belong
to a specific module, for example, IMX IOMUXC GPR and ANATOP.
With this driver, client can use generic regmap API to access registers
which are registered into syscon.

Reviewed-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Stephen Warren <swarren@wwwdotorg.org>
Signed-off-by: Dong Aisheng <dong.aisheng@linaro.org>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>
diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
index 856ec00..909d84b 100644
--- a/drivers/mfd/Kconfig
+++ b/drivers/mfd/Kconfig
@@ -1004,6 +1004,14 @@
 	  MFD controller. This controller embeds regulator and
 	  thermal devices for Freescale i.MX platforms.
 
+config MFD_SYSCON
+	bool "System Controller Register R/W Based on Regmap"
+	depends on OF
+	select REGMAP_MMIO
+	help
+	  Select this option to enable accessing system control registers
+	  via regmap.
+
 config MFD_PALMAS
 	bool "Support for the TI Palmas series chips"
 	select MFD_CORE