sparc32: add IOMMU chipset doc links

Signed-off-by: NBlue Swirl <blauwirbel@gmail.com>

hw/sun4m_iommu.c

 /*
- * QEMU SPARC iommu emulation
+ * QEMU Sun4m iommu emulation
  *
  * Copyright (c) 2003-2005 Fabrice Bellard
  *
@@ -35,6 +35,14 @@
 #define DPRINTF(fmt, ...)
 #endif
 
+/*
+ * I/O MMU used by Sun4m systems
+ *
+ * Chipset docs:
+ * "Sun-4M System Architecture (revision 2.0) by Chuck Narad", 950-1373-01,
+ * http://mediacast.sun.com/users/Barton808/media/Sun4M_SystemArchitecture_edited2.pdf
+ */
+
 #define IOMMU_NREGS         (4*4096/4)
 #define IOMMU_CTRL          (0x0000 >> 2)
 #define IOMMU_CTRL_IMPL     0xf0000000 /* Implementation */