exec.c: Provide full set of dummy wp remove functions in user-mode

We already provide dummy versions of the cpu_watchpoint_insert
and cpu_watchpoint_remove_all functions when CONFIG_USER_ONLY
is defined. Complete the set by providing cpu_watchpoint_remove
and cpu_watchpoint_remove_by_ref as well.

This allows target-* code using these functions to avoid
some ifdeffery.
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>
Reviewed-by: NRichard Henderson <rth@twiddle.net>

exec.c

@@ -572,6 +572,16 @@ void cpu_watchpoint_remove_all(CPUState *cpu, int mask)
 {
 }
 
+int cpu_watchpoint_remove(CPUState *cpu, vaddr addr, vaddr len,
+                          int flags)
+{
+    return -ENOSYS;
+}
+
+void cpu_watchpoint_remove_by_ref(CPUState *cpu, CPUWatchpoint *watchpoint)
+{
+}
+
 int cpu_watchpoint_insert(CPUState *cpu, vaddr addr, vaddr len,
                           int flags, CPUWatchpoint **watchpoint)
 {