Add dynamic writeback feature from 3.1

Conflicts:
	fs/block_dev.c
	fs/fs-writeback.c
	fs/internal.h
	fs/super.c
	include/linux/backing-dev.h
	include/linux/writeback.h
	include/trace/events/writeback.h
	mm/backing-dev.c
ALSA: hda/realtek - Fix Oops in alc_mux_select()

commit cce4aa378a049f4275416ee6302dd24f37b289df upstream.

When no imux is available (e.g. a single capture source),
alc_auto_init_input_src() may trigger an Oops due to the access to -1.
Add a proper zero-check to avoid it.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

Conflicts:
	sound/pci/hda/patch_realtek.c
Revert "Remove overclocking"

This reverts commit 8aa02a1ce30b296c9995411b29be9910bce0db19.
Revert "Add dynamic writeback feature from 3.1"

This reverts commit 6c0730dd8641c7c1f3a1cdc884b56f8a1440ffb7.