target-arm: Fix GDB breakpoint handling

GDB breakpoints have higher priority so they have to be checked first.
Should GDB breakpoint match, just return from the debug exception
handler.
Signed-off-by: NSergey Fedorov <serge.fdrv@gmail.com>
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

target-arm/op_helper.c

@@ -897,6 +897,12 @@ void arm_debug_excp_handler(CPUState *cs)
             }
         }
     } else {
+        uint64_t pc = is_a64(env) ? env->pc : env->regs[15];
+
+        if (cpu_breakpoint_test(cs, pc, BP_GDB)) {
+            return;
+        }
+
         if (check_breakpoints(cpu)) {
             bool same_el = (arm_debug_target_el(env) == arm_current_el(env));
             if (extended_addresses_enabled(env)) {