Rework meson pll driver to use clk_regmap and move meson8b, gxbb and
axg's clock using meson_clk_pll to clk_regmap.

This rework is not just about clk_regmap, there a serious clean-up of
the driver code:
* Add lock and reset field: Previously inferred from the n field.
* Simplify the reset logic: Code seemed to apply reset differently but
  in fact it was always the same -> assert reset, apply params,
  de-assert reset. The 2 lock checking loops have been kept for now, as
  they seem to be necessary.
* Do the sequence of init register pokes only at .init() instead of in
  .set_rate(). Redoing the init on every set_rate() is not necessary
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>