regulator: hi6421: Remove unused fields from struct hi6421_regulator_info

The valid_modes_mask and *dev are not used in this driver, remove them.
Current code uses devm_regulator_register, so we don't need *regulator in
hi6421_regulator_info. Use a local variable instead.

Also removes a few unnecessary inclusion of header files.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Mark Brown <broonie@linaro.org>