ALSA: Add ifdef CONFIG_GENERIC_ALLOCATOR for SNDRV_DMA_TYPE_IRAM code

It turned out that we can't use gen_pool_*() functions on archs
without CONFIG_GENERIC_ALLOCATOR (resulting in missing symbols), since
linux/genalloc.h doesn't provide dummy functions for all.  We'd be
able to fix linux/genalloc.h size, but I take an easier path for
now...

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index 513f095..b71be57 100644
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -3199,12 +3199,14 @@
 			     struct vm_area_struct *area)
 {
 	area->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP;
+#ifdef CONFIG_GENERIC_ALLOCATOR
 	if (substream->dma_buffer.dev.type == SNDRV_DMA_TYPE_DEV_IRAM) {
 		area->vm_page_prot = pgprot_writecombine(area->vm_page_prot);
 		return remap_pfn_range(area, area->vm_start,
 				substream->dma_buffer.addr >> PAGE_SHIFT,
 				area->vm_end - area->vm_start, area->vm_page_prot);
 	}
+#endif /* CONFIG_GENERIC_ALLOCATOR */
 #ifdef ARCH_HAS_DMA_MMAP_COHERENT
 	if (!substream->ops->page &&
 	    substream->dma_buffer.dev.type == SNDRV_DMA_TYPE_DEV)