minigbm: drv_bo_flush --> drv_bo_flush_or_unmap

There's no flush or invalidate mechnaism with the DRI interface,
so we'll have to support mapping and unmapping.

BUG=b:72972511
TEST=gbmtest passes in CQ

Change-Id: If3aef651f8549544ed4ed499e17f7f99c597974c
Reviewed-on: https://chromium-review.googlesource.com/990892
Commit-Ready: Gurchetan Singh <gurchetansingh@chromium.org>
Tested-by: Satyajit Sahu <satyajit.sahu@amd.com>
Reviewed-by: Joe Kniss <djmk@google.com>
Reviewed-by: Satyajit Sahu <satyajit.sahu@amd.com>
diff --git a/gbm.c b/gbm.c
index 25b4fa0..a720461 100644
--- a/gbm.c
+++ b/gbm.c
@@ -249,7 +249,7 @@
 PUBLIC void gbm_bo_unmap(struct gbm_bo *bo, void *map_data)
 {
 	assert(bo);
-	drv_bo_flush(bo->bo, map_data);
+	drv_bo_flush_or_unmap(bo->bo, map_data);
 }
 
 PUBLIC uint32_t gbm_bo_get_width(struct gbm_bo *bo)