Add 10-radeon.conf xorg.conf.d snippet

This instructs Xorg >= 1.16 to try loading the radeon driver for devices
managed by the radeon kernel driver, even if the ati wrapper driver
isn't available.

Copied from the amdgpu driver.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>

conf/10-radeon.conf

@@ -0,0 +1,5 @@
+Section "OutputClass"
+	Identifier "Radeon"
+	MatchDriver "radeon"
+	Driver "radeon"
+EndSection

conf/Makefile.am

@@ -0,0 +1,24 @@
+#  Copyright 2017 Advanced Micro Devices, Inc.
+#
+#  Permission is hereby granted, free of charge, to any person obtaining a
+#  copy of this software and associated documentation files (the "Software"),
+#  to deal in the Software without restriction, including without limitation
+#  on the rights to use, copy, modify, merge, publish, distribute, sub
+#  license, and/or sell copies of the Software, and to permit persons to whom
+#  the Software is furnished to do so, subject to the following conditions:
+#
+#  The above copyright notice and this permission notice (including the next
+#  paragraph) shall be included in all copies or substantial portions of the
+#  Software.
+#
+#  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+#  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+#  FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT.  IN NO EVENT SHALL
+#  ADAM JACKSON BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER
+#  IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+#  CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+
+if HAS_XORG_CONF_DIR
+dist_config_DATA = 10-radeon.conf
+endif