minigbm: add buffer bandwidth compression flag to gbm device

minigbm: add buffer bandwidth compression flag to gbm device

Read MINIGBM_DEBUG env var when creating a gbm driver
Store value as a flag inside driver
Avoid allocating compressed buffers in the backends
when the flag disables compression

BUG=b:172215587

Change-Id: Idbd6f0aebc1782c1bf5921a6438310a87212d1f8
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/minigbm/+/2535658
Tested-by: Pilar Molina Lopez <pmolinalopez@google.com>
Commit-Queue: Pilar Molina Lopez <pmolinalopez@google.com>
Reviewed-by: Gurchetan Singh <gurchetansingh@chromium.org>
Reviewed-by: Kristian H. Kristensen <hoegsberg@chromium.org>