minigbm: Add minimal buffer allocation support for msm

minigbm: Add minimal buffer allocation support for msm

Add minimal buffer allocation support using dumb_bo
for early enablement till the minigbm backend
implementation is avaialble for msm drv using
gem ioctls.

See CL:898422 for getting the DRV_MSM define in.

BUG=chromium:795946, b:72483556
TEST=Boot and see some graphics

Change-Id: Ieeb05923d756a3e4581a38cf6ce5cf406e2d197b
Reviewed-on: https://chromium-review.googlesource.com/897729
Commit-Ready: Douglas Anderson <dianders@chromium.org>
Tested-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>