The recent change (*) in the ALSA memalloc core allows us to drop the
special vmalloc-specific allocation and page handling.  This patch
coverts to the common code.
(*) 1fe7f397: ALSA: memalloc: Add vmalloc buffer allocation
                  support
    7e8edae3: ALSA: pcm: Handle special page mapping in the
                  default mmap handler

Since it requires the specific buffer type (SNDRV_DMA_TYPE_VMALLOC),
it's set in the pcm_new ops now.
Acked-by: NMark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20191108094641.20086-3-tiwai@suse.deSigned-off-by: NTakashi Iwai <tiwai@suse.de>