drm/i915/skl: Implementation of SKL display power well support

This patch implements core logic of SKL display power well.

v2: Addressed Imre's comments
	- Added respective DDIs under power well #1 and #2
	- Simplified repetitive code in power well programming

v3: Implemented Imre's comments
	- Further simplified power well programming
	- Made sure that PW 1 is enabled prior to PW 2

v4: Fix minor conflict with the the cherryview support (Damien)

v5: Add the PLL power domain to the always on power well (Damien)

v6: Disable BIOS power well (Imre)
    Use power well data for comparison (Imre)
    Put the PLL power domain into PW1 as its needed for CDCLK (Satheesh,
    Damien)

v7: Addressed Imre's comments
  - Lowered the time out to 1ms
  - Added parantheses in macro
  - Moved debug message and fixed wait_for interval

v8:
  - Add a WARN() when swiching on an unknown power well (Imre, done by Damien)
  - Whitespace fixes (spaces instead of tabs) (Damien)

v9: (Imre, done by Damien)
  - Merge the register definitions with this patch
  - Merge the MISC IO power well in this patch

v10: (Imre, done by Damien)

  - Define the Misc I/O power domains to be the power well 1 ones as Misc I/O
    needs to be enabled with PW1
  - Added Transcoder A and VGA domains to PW 2
  - Remove the MISC_IO power domains as well in the the always on
    domains definition
  - Move Misc I/O power well at the top of the power well list so it's turned
    on right after PW1.

Reviewed-by: Imre Deak <imre.deak@intel.com>
Signed-off-by: Satheeshakrishna M <satheeshakrishna.m@intel.com> (v3,v6,v7)
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>