Implement gbm_bo_import

Implement gbm_bo_import

We only support GBM_BO_IMPORT_FD for now.

BUG=chromium:541558
TEST=run unit test (graphics_Gbm)

Change-Id: I1232cfdb57efdbbe9c3243b74c4fc5bf20cd8c08
Signed-off-by: Stphane Marchesin <marcheu@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/311203
Commit-Ready: Ilja Friedel <ihf@chromium.org>
Tested-by: Stéphane Marchesin <marcheu@chromium.org>
Reviewed-by: Ilja Friedel <ihf@chromium.org>
Reviewed-by: David Reveman <reveman@chromium.org>
Reviewed-by: Haixia Shi <hshi@chromium.org>