common: Move some cache and MMU functions out of common.h

These functions belong in cpu_func.h. Another option would be cache.h
but that code uses driver model and we have not moved these cache
functions to use driver model. Since they are CPU-related it seems
reasonable to put them here.

Move them over.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/post/lib_powerpc/cpu.c b/post/lib_powerpc/cpu.c
index 6713039..8506fd6 100644
--- a/post/lib_powerpc/cpu.c
+++ b/post/lib_powerpc/cpu.c
@@ -5,6 +5,7 @@
  */
 
 #include <common.h>
+#include <cpu_func.h>
 
 /*
  * CPU test