gbm: Rename the DRI backend from gbm_dri.so to dri

A subsequent change will allow loading backends
from DSOs specified by the GBM_BACKEND environment
variable. The exact DSO name and path are derived
by the common loader code and will be of the form:

 <gbm_backend_path>/<GBM_BACKEND>_gbm.so

E.g., a user would set the environment variable to
"external" to load "external_gbm.so". Users will
also still be able to explicitly request any
builtin backends by name as well, so this change
helps keep the environment variable syntax
consistent between internal and external backends.

Signed-off-by: James Jones <jajones@nvidia.com>
Reviewed-by: Michel Dänzer <mdaenzer@redhat.com>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/9902>

src/gbm/main/backend.c

@@ -45,7 +45,7 @@ struct gbm_backend_desc {
 };
 
 static const struct gbm_backend_desc builtin_backends[] = {
-   { "gbm_dri.so", &gbm_dri_backend },
+   { "dri", &gbm_dri_backend },
 };
 
 static struct gbm_device *