[PATCH v6]: clk: Add common clock support for Mediatek MT8135 and MT8173

[Sascha Hauer <s.hauer@pengutronix.de>]

This patchset contains the initial common clock support for Mediatek SoCs.
Mediatek SoC's clock architecture comprises of various PLLs, dividers, muxes
and clock gates.

Sascha

Changes in v2:
- Re-ordered patchset. Fold include/dt-bindings and DT document in 1st patch.

Changes in v3:
- Rebase to 3.19-rc1.
- Refine code. Remove unneed functions, debug logs and comments, and fine tune
  error logs.

Changes in v4:
- Support MT8173 platform.
- Re-ordered patchset. driver/clk/Makefile in 2nd patch.
- Extract the common part definition(mtk_gate/mtk_pll/mtk_mux) from
  clk-mt8135.c/clk-mt8173.c to clk-mtk.c.
- Refine code. Rmove unnessacary debug information and unsed defines,
  add prefix "mtk_" for static functions.
- Remove flag CLK_IGNORE_UNUSED and set flag CLK_SET_RATE_PARENT on
  gate/mux/fixed-factor.
- Use spin_lock_irqsave(&clk_ops_lock, flags) instead of mtk_clk_lock.
- Example above include a node for the clock controller itself, followed
  by the i2c controller example above.

Changes in v5:
- Add reset controller support for pericfg/infracfg
- Use regmap for the gates
- remove now unnecessary spinlock for the gates
- Add PMIC wrapper support as of v3

Changes in v6:
- rework PLL support, only a fraction of original size now
- Move binding docs to Documentation/devicetree/bindings/arm/mediatek since
  the units are not really clock specific (they contain reset controllers)