drm/i915/fbc: Remove the FBC_RT_BASE setup for ILK/SNB

drm/i915/fbc: Remove the FBC_RT_BASE setup for ILK/SNB

We don't want to use the FBC hardware render tracking so let's not
enable it. To use the hw tracking properly we'd anyway need to
integrate this into the command submissing path as the register is
context saved, and if rendering happens via the ppgtt we'd have
to configure it with the ppgtt address instead of the ggtt address.
Easier to use software tracking instead.

Note that on pre-ilk we can't actually disable render tracking.
However we can't rely on it because it requires that DSPSURF to
match the render target address, and since we play tricks
with DSPSURF that may not be the case. Hence we shall rely on
software render tracking on all platforms.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191127201222.16669-5-ville.syrjala@linux.intel.com
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>