ALSA: memalloc: Support for non-coherent page allocation

Following to the addition of non-contiguous pages, this patch adds the
new contiguous non-coherent page allocation to the standard memalloc
helper.  Like the previous non-contig type, this non-coherent type is
also directional and requires the explicit sync, too.  Hence the
driver using this type of buffer may need to set
SNDRV_PCM_INFO_EXPLICIT_SYNC flag to the PCM hardware.info as well,
unless it's set up in the managed mode.

Link: https://lore.kernel.org/r/20211017074859.24112-3-tiwai@suse.de


Signed-off-by: Takashi Iwai <tiwai@suse.de>