drm/i915/fbc: don't use the frontbuffer tracking subsystem for flips

drm/i915/fbc: don't use the frontbuffer tracking subsystem for flips

Before this patch, page flips would call intel_frontbuffer_flip() and
intel_frontbuffer_flip_complete(), which would call intel_fbc_flush(),
which would call intel_fbc_update(). The problem is that drawing
operations also trigger intel_fbc_flush() calls, so it's not
guaranteed that we have the CRTC and FB locks grabbed when
intel_fbc_flush() happens, since the call trace may come from the
rendering path.

We're trying to make the FBC code grab the appropriate CRTC/FB locks,
so split the drawing and the flipping logic in order to achieve that
in later patches. So now the frontbuffer tracking code is just going
to be used for frontbuffer drawing, and intel_fbc_update() is going to
be used directly for actual page flips.

As a note, we don't need to call intel_fbc_flip() during the two
places where we call intel_frontbuffer_flip() since in one of them we
already have an intel_fbc_update() call, and in the other we have the
planes disabled.

Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1453210558-7875-7-git-send-email-paulo.r.zanoni@intel.com