drm/i915: handle FBC and self-refresh better

drm/i915: handle FBC and self-refresh better

commit ee25df2bc379728c45d81e04cf87984db1425edf upstream.

On 945, we need to avoid entering self-refresh if the compressor is
busy, or we may cause display FIFO underruns leading to ugly flicker.

Fixes fdo bug #24314, kernel bug #15043.

Tested-by: Alexander Lam <lambchop468@gmail.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Tested-by: Julien Cristau <jcristau@debian.org> (fd.o #25371)
Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>