Adds map_physmem function for MIPS.

Change-Id: I5a13525d779a5e683c1731dc383cceb30a3dd214
diff --git a/include/asm-mips/io.h b/include/asm-mips/io.h
index 857fb03..518f956 100755
--- a/include/asm-mips/io.h
+++ b/include/asm-mips/io.h
@@ -101,6 +101,24 @@
 #endif
 
 /*
+ * Given a physical address, return a virtual address that can be used to access
+ * the memory specified.
+ */
+static inline void *
+map_physmem(unsigned long paddr)
+{
+  return (void *) paddr;
+}
+
+/*
+ * Takes down mapping set up by map_physmem();
+ */
+static inline void unmap_physmem(void *vaddr)
+{
+  /* noop. */
+}
+
+/*
  * Change virtual addresses to physical addresses and vv.
  * These are trivial on the 1:1 Linux/MIPS mapping
  */