regulator: 88pm800: Use regulator_nodes/of_match in the descriptor

This patch is add regulator_nodes/of_match in the regulator
descriptor for using information from DT instead of specific codes.

With this patch, driver gets simplified,

  - No need to maintain "struct of_regulator_match" table
    and call of_regulator_match() fn.
  - No need for pm800_regulator_dt_init() fn, as it was only
    used for of_regulator_match().
  - probe() fn got simplified around regulator_config and regulator_desc
    initialization.

Signed-off-by: Vaibhav Hiremath <vaibhav.hiremath@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>