BaseTools: add centralized location for git config files

Before adding the git environment initialization script, add the
following files that will be pointed to after running said script:

- BaseTools/Conf/diff.order
- BaseTools/Conf/gitattributes

Signed-off-by: Leif Lindholm <leif.lindholm@linaro.org>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Bob Feng <bob.c.feng@intel.com>

BaseTools/Conf/diff.order

@@ -0,0 +1,13 @@
+#
+# Copyright (c) 2019, Linaro Ltd. All rights reserved.
+#
+# SPDX-License-Identifier: BSD-2-Clause-Patent
+#
+*.dec
+*.dsc.inc
+*.dsc
+*.fdf
+*.inf
+*.h
+*.vfr
+*.c