Add a b4 configuration file

b4 [1] is a convenient tool to manage patch series with mailing list
working flow.

Add a project default config file to match QEMU's mailing list conventions
as well as adopting differences on scripting.

Examples of b4:

    ```
    $ b4 prep --check
    Checking patches using:
      scripts/checkpatch.pl -q --terse --no-summary --mailback -

    ---
    Signed-off-by: Jiaxun Yang <[email protected]>
    ---
    Changes in v2:
    - Add lore masks (philmd) from:
      https://lore.kernel.org/qemu-devel/[email protected]/
    - Link to v1: https://lore.kernel.org/r/[email protected]
    ---
    ● cc5a4c890fed: Add a b4 configuration file
      ● checkpatch.pl: 27: WARNING: added, moved or deleted file(s), does MAINTAINERS need updating?
    ---
    Success: 0, Warning: 1, Error: 0
    ```

    ```
    $ b4 prep -c
    Will collect To: addresses using echo
    Will collect Cc: addresses using get_maintainer.pl
    Collecting To/Cc addresses
        + To: [email protected]
    ---
    You can trim/expand this list with: b4 prep --edit-cover
    Invoking git-filter-repo to update the cover letter.
    New history written in 0.02 seconds...
    Completely finished after 0.06 seconds
    ```

[1]: https://b4.docs.kernel.org/

Co-developed-by: Signed-off-by: Philippe Mathieu-Daudé <[email protected]>
Signed-off-by: Jiaxun Yang <[email protected]>
Message-ID: <[email protected]>
Signed-off-by: Philippe Mathieu-Daudé <[email protected]>

Author: FlyGoat

.b4-config

@@ -0,0 +1,14 @@
+#
+# Common b4 settings that can be used to send patches to QEMU upstream.
+# https://b4.docs.kernel.org/
+#
+
+[b4]
+    send-series-to = [email protected]
+    send-auto-to-cmd = echo
+    send-auto-cc-cmd = scripts/get_maintainer.pl --noroles --norolestats --nogit --nogit-fallback
+    am-perpatch-check-cmd = scripts/checkpatch.pl -q --terse --no-summary --mailback -
+    prep-perpatch-check-cmd = scripts/checkpatch.pl -q --terse --no-summary --mailback -
+    searchmask = https://lore.kernel.org/qemu-devel/?x=m&t=1&q=%s
+    linkmask = https://lore.kernel.org/qemu-devel/%s
+    linktrailermask = Message-ID: <%s>