mfd: sec: Remove sec_reg* regmap helpers

Remove sec_reg* helpers as they are not used anymore. These helpers were
error-prone as they mixed u8 with unsigned int and they changed order of
some of parameters (val and mask in sec_reg_update()).

Also the helpers didn't give any way of useful abstraction as they just
called corresponding regmap function.

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>