cleanup: rename armv4_5 to arm for readability

Nothing more than a name change, just to make reading
the code a bit simpler.

Change-Id: I73a16b7302b48ce07d9688162955aae71d11eb45
Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-on: http://openocd.zylin.com/390
Tested-by: jenkins
Reviewed-by: Øyvind Harboe <oyvindharboe@gmail.com>

src/target/arm.h

@@ -197,7 +197,7 @@ struct arm_reg {
 	int num;
 	enum arm_mode mode;
 	struct target *target;
-	struct arm *armv4_5_common;
+	struct arm *arm;
 	uint32_t value;
 };