mainboard: Add ASRock H81M-HDS

Tested with GRUB 2.02 as a payload, booting Debian GNU/Linux 9.5 with
kernel 4.9.

This board works quite well under coreboot. A list of what works and
what doesn't can be found in the documentation part of this commit.

The file `data.vbt` matches the VBT in the latest stable version of the
vendor firmware (version 2.20).

Change-Id: I53483bb9fa335e86e85dfc487fef03fce4b85e2a
Signed-off-by: Tristan Corrick <tristan@corrick.kiwi>
Reviewed-on: https://review.coreboot.org/29390
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Rudolph <siro@das-labor.org>
diff --git a/src/mainboard/asrock/h81m-hds/Makefile.inc b/src/mainboard/asrock/h81m-hds/Makefile.inc
new file mode 100644
index 0000000..94bd1cfe
--- /dev/null
+++ b/src/mainboard/asrock/h81m-hds/Makefile.inc
@@ -0,0 +1,17 @@
+##
+## This file is part of the coreboot project.
+##
+## Copyright (C) 2018 Tristan Corrick <tristan@corrick.kiwi>
+##
+## This program is free software: you can redistribute it and/or modify
+## it under the terms of the GNU General Public License as published by
+## the Free Software Foundation, either version 2 of the License, or
+## (at your option) any later version.
+##
+## This program is distributed in the hope that it will be useful,
+## but WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+## GNU General Public License for more details.
+##
+
+ramstage-$(CONFIG_MAINBOARD_USE_LIBGFXINIT) += gma-mainboard.ads