util/u_trace: include the generated header first

This is a good practice to make sure the generated header is
self-contained (no missing includes, declarations, etc.).

Remove unnecessary SOURCE header scope from the default.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/18238>

src/util/perf/u_trace.py

@@ -120,13 +120,13 @@ class TracepointArg(object):
 HEADERS = []
 
 class HeaderScope(IntEnum):
-   HEADER = (1 << 0)
-   SOURCE = (1 << 1)
+    HEADER = (1 << 0)
+    SOURCE = (1 << 1)
 
 class Header(object):
     """Class that represents a header file dependency of generated tracepoints
     """
-    def __init__(self, hdr, scope=HeaderScope.HEADER|HeaderScope.SOURCE):
+    def __init__(self, hdr, scope=HeaderScope.HEADER):
         """Parameters:
 
         - hdr: the required header path
@@ -301,12 +301,12 @@ src_template = """\
  * IN THE SOFTWARE.
  */
 
+#include "${hdr}"
+
 % for header in HEADERS:
 #include "${header.hdr}"
 % endfor
 
-#include "${hdr}"
-
 #define __NEEDS_TRACE_PRIV
 #include "util/debug.h"
 #include "util/perf/u_trace_priv.h"