iio: adc: exynos_adc: Add exynos_adc_data structure to improve readability

This patchset add 'exynos_adc_data' structure which includes some functions
to control ADC operation and specific data according to ADC version (v1 or v2).

Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Reviewed-by: Naveen Krishna Chatradhi <ch.naveen@samsung.com>
Reviewed-by: Tomasz Figa <t.figa@samsung.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>