regulator: anatop-regulator: Convert to use syscon to access anatop register

Using syscon to access anatop register.

Acked-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>