regulator: s5m8767: Add symbols for hard-coded DVS_RAMP register

Add symbols for hard-coded values of BUCK_RAMP field in DVS_RAMP
register. This simplifies a little the code as register update is called
only once.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Mark Brown <broonie@linaro.org>