drm/i915/display/fbc: Disable fbc by default on TGL

Fbc is causing random underruns in CI execution on TGL platforms.
Disabling the same while the problem is being debugged and analyzed.

v2: Moved the check below the module param check (Ville)

Cc: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Uma Shankar <uma.shankar@intel.com>
Acked-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200716145857.6911-1-uma.shankar@intel.com


Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>