[ARM] Fix consistent_alloc()

The old consistent memory allocator, which sat behind
dma_coherent_alloc() and pci_consistent_alloc() was completely unable
to handle allocations from interrupt context because we traditionally
used ioremap, which in turn:
  - allocates memory using GFP_KERNEL for the vm_struct
    and the page tables themselves.
  - calls get_vm_area, which uses write_lock, and therefore
    is unsafe to call from interrupt context.

In order to address this issue, a new consistent_alloc() which avoids
the above issues has been implemented.  Essentially, we set aside
a section of the kernel VM space, and pre-allocate page tables to
cover this area.  We allocate "consistent" memory within this region.

The handling of the allocation is designed to be generic; it should
be possible to replace the vmalloc(), ioremap() and module_alloc()
without too much hastle, but that would clearly be a 2.7 thing at
this stage.

drivers/video/sa1100fb.c

@@ -1642,7 +1642,7 @@ static int __init sa1100fb_map_video_memory(struct sa1100fb_info *fbi)
 	 */
 	fbi->map_size = PAGE_ALIGN(fbi->fb.fix.smem_len + PAGE_SIZE);
 	fbi->map_cpu = consistent_alloc(GFP_KERNEL, fbi->map_size,
-					&fbi->map_dma);
+					&fbi->map_dma, PTE_BUFFERABLE);
 
 	if (fbi->map_cpu) {
 		fbi->fb.screen_base = fbi->map_cpu + PAGE_SIZE;

include/asm-arm/dma-mapping.h

@@ -14,7 +14,7 @@
  * devices.  This is the "generic" version.  The PCI specific version
  * is in pci.h
  */
-extern void *consistent_alloc(int gfp, size_t size, dma_addr_t *handle);
+extern void *consistent_alloc(int gfp, size_t size, dma_addr_t *handle, unsigned long flags);
 extern void consistent_free(void *vaddr, size_t size, dma_addr_t handle);
 extern void consistent_sync(void *kaddr, size_t size, int rw);
 
@@ -84,12 +84,12 @@ static inline int dma_is_consistent(dma_addr_t handle)
 static inline void *
 dma_alloc_coherent(struct device *dev, size_t size, dma_addr_t *handle)
 {
-	int gfp = GFP_KERNEL;
+	int gfp = GFP_ATOMIC;
 
 	if (dev == NULL || dmadev_is_sa1111(dev) || *dev->dma_mask != 0xffffffff)
 		gfp |= GFP_DMA;
 
-	return consistent_alloc(gfp, size, handle);
+	return consistent_alloc(gfp, size, handle, 0);
 }
 
 /**

include/asm-arm/pci.h

@@ -40,13 +40,13 @@ static inline void pcibios_penalize_isa_irq(int irq)
 static inline void *
 pci_alloc_consistent(struct pci_dev *hwdev, size_t size, dma_addr_t *handle)
 {
-	int gfp = GFP_KERNEL;
+	int gfp = GFP_ATOMIC;
 
 	if (hwdev == NULL || pcidev_is_sa1111(hwdev) ||
 	    hwdev->dma_mask != 0xffffffff)
 		gfp |= GFP_DMA;
 
-	return consistent_alloc(gfp, size, handle);
+	return consistent_alloc(gfp, size, handle, 0);
 }
 
 static inline void