Detect DRI nodes based on name rather than file type to handle FreeBSD
which has symbolic links to the actual device node.

diff -u SDL2-2.0.9.orig/src/video/kmsdrm/SDL_kmsdrmvideo.c SDL2-2.0.9/src/video/kmsdrm/SDL_kmsdrmvideo.c
--- SDL2-2.0.9.orig/src/video/kmsdrm/SDL_kmsdrmvideo.c	2019-05-07 17:17:44.381776000 +0200
+++ SDL2-2.0.9/src/video/kmsdrm/SDL_kmsdrmvideo.c	2018-10-31 16:07:22.000000000 +0100
@@ -95,7 +95,7 @@
     folder = opendir(KMSDRM_DRI_PATH);
     if (folder) {
         while ((res = readdir(folder))) {
-            if (res->d_namlen > 4 && strncmp(res->d_name, "card", 4)) {
+            if (res->d_type == DT_CHR) {
                 devcount++;
             }
         }