Revert "ALSA: pcm: Use SG-buffer only when direct DMA is available"

This reverts commit 3ad796cb ("ALSA: pcm: Use SG-buffer only when
direct DMA is available") also the modification commit 467fd0e8
("ALSA: pcm: Fix build error on m68k and others").

Poking the DMA internal helper is a layer violation, so we should
avoid that.  Meanwhile the actual bug has been addressed by the
Kconfig fix in commit dbed452a

 ("dma-pool: decouple DMA_REMAP from
DMA_COHERENT_POOL"), so we can live without this hack.

Link: https://lore.kernel.org/r/20200717064130.22957-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>