Import minigbm

Minigbm is a gbm implementation for a few DRM targets. Currently the
targets are:
- cirrus
- exynos
- gma500
- i915
- rockchip
- tegra
- udl

Right some targets are controlled with GBM_{TARGET} flags. I would
like to get to a place where we can just build all the targets in a
single library, but we need the drm headers for all targets for that
to happen so this needs more thinking.

BUG=chromium:394868,chromium:402597,chromium:413947,chromium:412508
TEST=unit tests, which I will need to import later

Signed-off-by: Stéphane Marchesin <marcheu@chromium.org>
Change-Id: I36ae07f2a59827a807e19e1432891ca196b28803
Reviewed-on: https://chromium-review.googlesource.com/218030
16 files changed