ARM922T's icache isn't coherent with its dcache, so we need to ensure that its flushed before changing codecs. Playback takes care of this for us, but only if we define cache coherency functions. Do that. Also, add a comment explaining that MMU functions need to be included so that other people don't spend hours chasing them in the future.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@21647 a1c6a512-1295-4272-9138-f99709370657

firmware/target/arm/as3525/system-target.h

@@ -22,6 +22,7 @@
 #define SYSTEM_TARGET_H
 
 #include "system-arm.h"
+#include "mmu-arm.h"
 
 #include "clock-target.h" /* CPUFREQ_* are defined here */
 

firmware/target/arm/mmu-arm.h

@@ -18,6 +18,11 @@
  * KIND, either express or implied.
  *
  ****************************************************************************/
+
+/*  This file MUST be included in your system-target.h file if you want arm
+ *  cache coherence functions to be called (I.E. during codec load, etc).   
+ */
+
 #ifndef MMU_ARM_H
 #define MMU_ARM_H