maintainers: Add myself as a OpenBSD maintainer

Add myself as an OpenBSD maintainer and add OpenBSD as maintained.

Signed-off-by: Brad Smith <brad@comstyle.com>
Reviewed-by: Kamil Rytarowski <n54@gmx.com>
Message-id: 20180216164620.GA53727@humpty.home.comstyle.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
diff --git a/configure b/configure
index ed45a3c..39f3a43 100755
--- a/configure
+++ b/configure
@@ -760,6 +760,7 @@
   audio_drv_list="sdl"
   audio_possible_drivers="sdl"
   HOST_VARIANT_DIR="openbsd"
+  supported_os="yes"
 ;;
 Darwin)
   bsd="yes"