drm/i915/fbc: FBC causes display flicker when VT-d is enabled on Skylake

Erratum SKL075: Display Flicker May Occur When Both VT-d And FBC Are Enabled

"Display flickering may occur when both FBC (Frame Buffer Compression)
and VT - d (Intel® Virtualization Technology for Directed I/O) are enabled
and in use by the display controller."

Ville found the w/a name in the database:
WaFbcTurnOffFbcWhenHyperVisorIsUsed:skl,bxt and also dug out that it
affects Broxton.

v2: Log when the quirk is applied.
v3: Ensure i915.enable_fbc is false when !HAS_FBC()
v4: Fix function name after rebase
v5: Add Broxton to the workaround

Note for backporting to stable, we need to add
  #define mkwrite_device_info(ptr) \
	((struct intel_device_info *)INTEL_INFO(ptr))

Signed-off-by: Chris Wilson <[email protected]>
Cc: Paulo Zanoni <[email protected]>
Cc: Ville Syrjälä <[email protected]>
Reviewed-by: Ville Syrjälä <[email protected]>
Cc: [email protected]
Link: http://patchwork.freedesktop.org/patch/msgid/[email protected]

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