armv7m: use generic arm::core_mode

To simplify things change over to using the generic core_mode struct rather
than maintaining a armv7m specific one.

Change-Id: Ibf32b785d896fef4f33307fabe0d8eb266f7086f
Signed-off-by: Spencer Oliver <spen@spen-soft.co.uk>
Reviewed-on: http://openocd.zylin.com/966
Tested-by: jenkins
Reviewed-by: Andreas Fritiofson <andreas.fritiofson@gmail.com>

src/target/arm.h

@@ -63,9 +63,9 @@ enum arm_mode {
 	ARM_MODE_UND = 27,
 	ARM_MODE_SYS = 31,
 
-	ARM_MODE_THREAD,
-	ARM_MODE_USER_THREAD,
-	ARM_MODE_HANDLER,
+	ARM_MODE_THREAD = 0,
+	ARM_MODE_USER_THREAD = 1,
+	ARM_MODE_HANDLER = 2,
 
 	ARM_MODE_ANY = -1
 };