x86-64, docs, mm: Add vsyscall range to virtual address space layout

Add the end of the virtual address space to its layout documentation.
Signed-off-by: Borislav Petkov <bp@alien8.de>
Link: http://lkml.kernel.org/r/1362428180-8865-4-git-send-email-bp@alien8.deSigned-off-by: H. Peter Anvin <hpa@linux.intel.com>

Documentation/x86/x86_64/mm.txt

@@ -13,7 +13,9 @@ ffffe90000000000 - ffffe9ffffffffff (=40 bits) hole
 ffffea0000000000 - ffffeaffffffffff (=40 bits) virtual memory map (1TB)
 ... unused hole ...
 ffffffff80000000 - ffffffffa0000000 (=512 MB)  kernel text mapping, from phys 0
-ffffffffa0000000 - fffffffffff00000 (=1536 MB) module mapping space
+ffffffffa0000000 - ffffffffff5fffff (=1525 MB) module mapping space
+ffffffffff600000 - ffffffffffdfffff (=8 MB) vsyscalls
+ffffffffffe00000 - ffffffffffffffff (=2 MB) unused hole
 
 The direct mapping covers all memory in the system up to the highest
 memory address (this means in some cases it can also include PCI memory