minigbm: Opening new fd for dri backend

minigbm: Opening new fd for dri backend

Dri backend is not used for the all use flags. When same fd is
shared between dri backend and the minigbm drv, they end up using the
same kernel DRI context.

BUG=b:111081134
TEST=cheets_SurfaceComposition
     graphics_Gbm
     graphics_Gralloc

Change-Id: I47ae12391acfc9c947e8281de11472fcdf5dec5b
Signed-off-by: Satyajit Sahu <satyajit.sahu@amd.com>
Reviewed-on: https://chromium-review.googlesource.com/1164972
Tested-by: Deepak Sharma <deepak.sharma@amd.com>
Reviewed-by: Tomasz Figa <tfiga@chromium.org>
Reviewed-by: Gurchetan Singh <gurchetansingh@chromium.org>