selftests: breakpoints: fix compile error on breakpoint_test_arm64

The current mainline breakpoints test for arm64 fails to compile with

breakpoint_test_arm64.c: In function ‘set_watchpoint’:
breakpoint_test_arm64.c:97:28: error: storage size of ‘dreg_state’ isn’t known
  struct user_hwdebug_state dreg_state;

Adding a direct include for asm/ptrace.h helps it to build, and passes
the test on mainline on hikey.
Signed-off-by: NSumit Semwal <sumit.semwal@linaro.org>
Signed-off-by: NShuah Khan <shuahkh@osg.samsung.com>

tools/testing/selftests/breakpoints/breakpoint_test_arm64.c

@@ -19,6 +19,7 @@
 
 #define _GNU_SOURCE
 
+#include <asm/ptrace.h>
 #include <sys/types.h>
 #include <sys/wait.h>
 #include <sys/ptrace.h>