Update DMA-mapping documentation

A couple of updates haven't considered whether the documentation makes
sense as a whole any more.  Three changes here:

 - Remove the reference to the "DAC Addressing for Address Space Hungry
   Devices" section which was deleted by Jan Beulich.
 - Remove the comment about DMA_24BIT_MASK which became obsolete when
   Tobias Klauser changed the code to actually use DMA_24BIT_MASK.
 - Remove the section "64-bit DMA and DAC cycle support" since it's
   fully covered above, and contains a reference to the section deleted
   by Jan.
Signed-off-by: Matthew Wilcox <willy@linux.intel.com>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/DMA-mapping.txt

@@ -189,12 +189,6 @@ smaller mask as pci_set_dma_mask(). However for the rare case that a
 device driver only uses consistent allocations, one would have to
 check the return value from pci_set_consistent_dma_mask().
 
-If your 64-bit device is going to be an enormous consumer of DMA
-mappings, this can be problematic since the DMA mappings are a
-finite resource on many platforms.  Please see the "DAC Addressing
-for Address Space Hungry Devices" section near the end of this
-document for how to handle this case.
-
 Finally, if your device can only drive the low 24-bits of
 address during PCI bus mastering you might do something like:
 
@@ -203,8 +197,6 @@ address during PCI bus mastering you might do something like:
 		       "mydev: 24-bit DMA addressing not available.\n");
 		goto ignore_this_device;
 	}
-[Better use DMA_24BIT_MASK instead of 0x00ffffff.
-See linux/include/dma-mapping.h for reference.]
 
 When pci_set_dma_mask() is successful, and returns zero, the PCI layer
 saves away this mask you have provided.  The PCI layer will use this
@@ -652,18 +644,6 @@ It is planned to completely remove virt_to_bus() and bus_to_virt() as
 they are entirely deprecated.  Some ports already do not provide these
 as it is impossible to correctly support them.
 
-		64-bit DMA and DAC cycle support
-
-Do you understand all of the text above?  Great, then you already
-know how to use 64-bit DMA addressing under Linux.  Simply make
-the appropriate pci_set_dma_mask() calls based upon your cards
-capabilities, then use the mapping APIs above.
-
-It is that simple.
-
-Well, not for some odd devices.  See the next section for information
-about that.
-
 		Optimizing Unmap State Space Consumption
 
 On many platforms, pci_unmap_{single,page}() is simply a nop.