target: less implicit inclusion of "etm.h"

Don't include it in more headers than necessary; just
use it in the few files that actually need it.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>

src/target/arm7_9_common.h

@@ -30,6 +30,7 @@
 #define ARM7_9_COMMON_H
 
 #include "armv4_5.h"
+#include "arm_jtag.h"
 
 #define	ARM7_9_COMMON_MAGIC 0x0a790a79 /**< */