[lldb][test] Mark some more watchpoint tests

Noticed when testing with qemu-aarch64 that does not support watchpoints.
diff --git a/lldb/test/API/functionalities/watchpoint/categories b/lldb/test/API/functionalities/watchpoint/categories
new file mode 100644
index 0000000..97934fb
--- /dev/null
+++ b/lldb/test/API/functionalities/watchpoint/categories
@@ -0,0 +1,2 @@
+watchpoint
+