vf610 has two ADC controllers, and vf610-twr board ADC0_SE5 pin connect
to sliding rheostat for ADC test, other ADC pins connect to connectors for
future use.
Add support for ADC0_SE5.
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: Shawn Guo <shawn.guo@linaro.org>