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>

configure.ac

@@ -79,6 +79,20 @@ PKG_CHECK_MODULES(XEXT, [xextproto >= 7.0.99.1],
                   HAVE_XEXTPROTO_71="no")
 AM_CONDITIONAL(HAVE_XEXTPROTO_71, [ test "$HAVE_XEXTPROTO_71" = "yes" ])
 
+# Section "OutputClass" is only supported as of xserver 1.16
+PKG_CHECK_EXISTS([xorg-server >= 1.16],
+		 [sysconfigdir=`$PKG_CONFIG --variable=sysconfigdir xorg-server`],
+		 [sysconfigdir=""])
+AM_CONDITIONAL(HAS_XORG_CONF_DIR, [test "x$sysconfigdir" != "x"])
+
+# Define a configure option for an alternate X Server configuration directory
+AC_ARG_WITH(xorg-conf-dir,
+            AS_HELP_STRING([--with-xorg-conf-dir=DIR],
+                           [Default xorg.conf.d directory [[default=${prefix}/share/X11/xorg.conf.d]]]),
+            [configdir="$withval"],
+            [configdir='${prefix}/share/X11/xorg.conf.d'])
+AC_SUBST(configdir)
+
 AC_ARG_ENABLE([udev],
 		AS_HELP_STRING([--disable-udev], [Disable libudev support [default=auto]]),
 		[enable_udev="$enableval"],
@@ -265,6 +279,7 @@ AC_CONFIG_FILES([
                 Makefile
                 src/Makefile
                 man/Makefile
+                conf/Makefile
 ])
 AC_OUTPUT
 
@@ -276,6 +291,7 @@ echo "        prefix:              $prefix"
 echo "        exec_prefix:         $exec_prefix"
 echo "        libdir:              $libdir"
 echo "        includedir:          $includedir"
+echo "        configdir:           $configdir"
 
 echo ""
 echo "        CFLAGS:              $CFLAGS"