drm/i915: Adjust CDCLK accordingly to our DBuf bw needs

According to BSpec max BW per slice is calculated using formula
Max BW = CDCLK * 64. Currently when calculating min CDCLK we
account only per plane requirements, however in order to avoid
FIFO underruns we need to estimate accumulated BW consumed by
all planes(ddb entries basically) residing on that particular
DBuf slice. This will allow us to put CDCLK lower and save power
when we don't need that much bandwidth or gain additional
performance once plane consumption grows.

v2: - Fix long line warning
    - Limited new DBuf bw checks to only gens >= 11

v3: - Lets track used Dbuf bw per slice and per crtc in bw state
      (or may be in DBuf state in future), that way we don't need
      to have all crtcs in state and those only if we detect if
      are actually going to change cdclk, just same way as we
      do with other stuff, i.e intel_atomic_serialize_global_state
      and co. Just as per Ville's paradigm.
    - Made dbuf bw calculation procedure look nicer by introducing
      for_each_dbuf_slice_in_mask - we often will now need to iterate
      slices using mask.
    - According to experimental results CDCLK * 64 accounts for
      overall bandwidth across all dbufs, not per dbuf.

v4: - Fixed missing const(Ville)
    - Removed spurious whitespaces(Ville)
    - Fixed local variable init(reduced scope where not needed)
    - Added some comments about data rate for planar formats
    - Changed struct intel_crtc_bw to intel_dbuf_bw
    - Moved dbuf bw calculation to intel_compute_min_cdclk(Ville)

v5: - Removed unneeded macro

v6: - Prevent too frequent CDCLK switching back and forth:
      Always switch to higher CDCLK when needed to prevent bandwidth
      issues, however don't switch to lower CDCLK earlier than once
      in 30 minutes in order to prevent constant modeset blinking.
      We could of course not switch back at all, however this is
      bad from power consumption point of view.

v7: - Fixed to track cdclk using bw_state, modeset will be now
      triggered only when CDCLK change is really needed.

v8: - Lock global state if bw_state->min_cdclk is changed.
    - Try getting bw_state only if there are crtcs in the commit
      (need to have read-locked global state)

v9: - Do not do Dbuf bw check for gens < 9 - triggers WARN
      as ddb_size is 0.

v10: - Lock global state for older gens as well.

v11: - Define new bw_calc_min_cdclk hook, instead of using
       a condition(Manasi Navare)

v12: - Fixed rebase conflict

v13: - Added spaces after declarations to make checkpatch happy.

Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200520150058.16123-1-stanislav.lisovskiy@intel.com