regulator: s5m8767: Modify parse_dt function to parse data related to ramp

This patch parse 'buck[2-4]_ramp_enable and buck_ramp_delay' platform data
from dts file.

Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Mark Brown <broonie@linaro.org>