minigbm: refactor and rename mapping struct

minigbm: refactor and rename mapping struct

Since some drivers (AMDGPU, Tegra) may have to do expensive tiling
and detiling operations, we should try to take advantage of the
access regions passed in by gralloc and gbm. Let's refactor struct
map_data so we can separate the actual mapping and access region.

Here is the Coccinelle rule used in this change:

@@ struct map_info *M; @@
-   (M)
+   M->vma

In addition, struct map_data was also renamed to struct mapping.

BUG=chromium:764871
TEST= mmap_test -g on Kevin

Change-Id: Idb094aa3b5f81e45ce3a2f4fb2d9bf8fba32bf29
Reviewed-on: https://chromium-review.googlesource.com/758144
Commit-Ready: Gurchetan Singh <gurchetansingh@chromium.org>
Tested-by: Gurchetan Singh <gurchetansingh@chromium.org>
Reviewed-by: Joe Kniss <djmk@google.com>
Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>