ALSA: pcm: use dma_can_mmap() to check if a device supports dma_mmap_*

Replace the local hack with the dma_can_mmap helper to check if
a given device supports mapping DMA allocations to userspace.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Takashi Iwai <tiwai@suse.de>