mfd: simple-mfd-i2c: Add a Kconfig name

Add a Kconfig name to the "Simple Multi-Functional Device support (I2C)"
device so that it can be enabled via menuconfig.
Signed-off-by: Alistair Francis <alistair@alistair23.me>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/Kconfig

@@ -1188,7 +1188,7 @@ config MFD_SI476X_CORE
 	  module will be called si476x-core.
 
 config MFD_SIMPLE_MFD_I2C
-	tristate
+	tristate "Simple Multi-Functional Device support (I2C)"
 	depends on I2C
 	select MFD_CORE
 	select REGMAP_I2C