iio:adc:imx: add Freescale Vybrid vf610 adc driver

Add Freescale Vybrid vf610 adc driver. The driver only support
ADC software trigger.

VF610 ADC device documentation is available at below reference manual
(chapter 37):
http://cache.freescale.com/files/32bit/doc/ref_manual/VYBRIDRM.pdf?
fpsp=1&WT_TYPE=Reference%20Manuals&WT_VENDOR=FREESCALE&WT_FILE_FORMAT
=pdf&WT_ASSET=Documentation

CC: Shawn Guo <shawn.guo@linaro.org>
CC: Jonathan Cameron <jic23@kernel.org>
CC: Mark Rutland <mark.rutland@arm.com>
CC: Otavio Salvador <otavio@ossystems.com.br>
CC: Peter Meerwald <pmeerw@pmeerw.net>
CC: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Fugang Duan <B38611@freescale.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>

drivers/iio/adc/Kconfig

@@ -197,6 +197,16 @@ config TWL6030_GPADC
 	  This driver can also be built as a module. If so, the module will be
 	  called twl6030-gpadc.
 
+config VF610_ADC
+	tristate "Freescale vf610 ADC driver"
+	depends on OF
+	help
+	  Say yes here to support for Vybrid board analog-to-digital converter.
+	  Since the IP is used for i.MX6SLX, the driver also support i.MX6SLX.
+
+	  This driver can also be built as a module. If so, the module will be
+	  called vf610_adc.
+
 config VIPERBOARD_ADC
 	tristate "Viperboard ADC support"
 	depends on MFD_VIPERBOARD && USB

drivers/iio/adc/Makefile

@@ -21,4 +21,5 @@ obj-$(CONFIG_NAU7802) += nau7802.o
 obj-$(CONFIG_TI_ADC081C) += ti-adc081c.o
 obj-$(CONFIG_TI_AM335X_ADC) += ti_am335x_adc.o
 obj-$(CONFIG_TWL6030_GPADC) += twl6030-gpadc.o
+obj-$(CONFIG_VF610_ADC) += vf610_adc.o
 obj-$(CONFIG_VIPERBOARD_ADC) += viperboard_adc.o