ALSA: aloop: Convert to the common vmalloc memalloc

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

Link: https://lore.kernel.org/r/20191105151856.10785-10-tiwai@suse.deSigned-off-by: Takashi Iwai <tiwai@suse.de>

sound/drivers/aloop.c

@@ -576,8 +576,7 @@ static void loopback_runtime_free(struct snd_pcm_runtime *runtime)
 static int loopback_hw_params(struct snd_pcm_substream *substream,
 			      struct snd_pcm_hw_params *params)
 {
-	return snd_pcm_lib_alloc_vmalloc_buffer(substream,
-						params_buffer_bytes(params));
+	return snd_pcm_lib_malloc_pages(substream, params_buffer_bytes(params));
 }
 
 static int loopback_hw_free(struct snd_pcm_substream *substream)
@@ -589,7 +588,7 @@ static int loopback_hw_free(struct snd_pcm_substream *substream)
 	mutex_lock(&dpcm->loopback->cable_lock);
 	cable->valid &= ~(1 << substream->stream);
 	mutex_unlock(&dpcm->loopback->cable_lock);
-	return snd_pcm_lib_free_vmalloc_buffer(substream);
+	return snd_pcm_lib_free_pages(substream);
 }
 
 static unsigned int get_cable_index(struct snd_pcm_substream *substream)
@@ -765,7 +764,6 @@ static const struct snd_pcm_ops loopback_pcm_ops = {
 	.prepare =	loopback_prepare,
 	.trigger =	loopback_trigger,
 	.pointer =	loopback_pointer,
-	.page =		snd_pcm_lib_get_vmalloc_page,
 };
 
 static int loopback_pcm_new(struct loopback *loopback,
@@ -780,6 +778,8 @@ static int loopback_pcm_new(struct loopback *loopback,
 		return err;
 	snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_PLAYBACK, &loopback_pcm_ops);
 	snd_pcm_set_ops(pcm, SNDRV_PCM_STREAM_CAPTURE, &loopback_pcm_ops);
+	snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_VMALLOC,
+					      NULL, 0, 0);
 
 	pcm->private_data = loopback;
 	pcm->info_flags = 0;