drm/i915: Display WA #1185 WaDisableDARBFClkGating:cnl, glk

drm/i915: Display WA #1185 WaDisableDARBFClkGating:cnl, glk

Display is not sending a PMRsp when a PMReq is received
at the same time that all planes are turned off.
State machine in the dcprunit is stuck in the WAIT4DONE
state which means that there is no fill_done.

WA: disable arbiter clock gating, set bit [27] of 0x46530

v2: As Ville pointed out, based on the description the issue
    can happen when disabling the planes, similar to
    WaRsPkgCStateDisplayPMReq:hsw
    Also description of the issue was updated on commit
    message to make it more clear that we need this
    earlier.
v3: Restore comment about possibility to system hang
    to where we are sure about it, without speculation. (Ville).
v4: Remove doubled sob. Actually do v3 changes :/

Cc: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
Cc: Imre Deak <imre.deak@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171111000319.5040-1-rodrigo.vivi@intel.com