minigbm: cros_gralloc: simplify getting the drm format string

Can we do this.

BUG=none
TEST=compile

Change-Id: If9488038f1eb77b92e37d6daa99c8bea495315c8
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/minigbm/+/2451522
Tested-by: Gurchetan Singh <gurchetansingh@chromium.org>
Reviewed-by: Jason Macnak <natsu@google.com>
Reviewed-by: Gurchetan Singh <gurchetansingh@chromium.org>
Commit-Queue: Gurchetan Singh <gurchetansingh@chromium.org>
diff --git a/cros_gralloc/cros_gralloc_helpers.h b/cros_gralloc/cros_gralloc_helpers.h
index 36f86ef..a43833d 100644
--- a/cros_gralloc/cros_gralloc_helpers.h
+++ b/cros_gralloc/cros_gralloc_helpers.h
@@ -24,4 +24,6 @@
 
 int32_t cros_gralloc_sync_wait(int32_t fence, bool close_fence);
 
+std::string get_drm_format_string(uint32_t drm_format);
+
 #endif