minigbm: replace DRM_FORMAT_MOD_INVALID with DRM_FORMAT_MOD_LINEAR

minigbm: replace DRM_FORMAT_MOD_INVALID with DRM_FORMAT_MOD_LINEAR

CL:737409 replaced DRM_FORMAT_MOD_NONE with DRM_FORMAT_MOD_INVALID in
struct kms_item. We use drv_query_kms() to add the scanout flag to most
buffer combinations. That means anything with DRM_FORMAT_MOD_LINEAR
will not get the scanout flag, since drv_query_kms returns combinations
with DRM_FORMAT_MOD_INVALID. This leads to artifacts in the zero latency
app, since we end up picking a X-tiled buffer since we don't advertise
a linear buffer with scanout.

Since all hardware can scanout linear buffers, replace DRM_FORMAT_MOD_INVALID
with DRM_FORMAT_MOD_LINEAR.

BUG=chromium:762324
TEST=no overlay artifacts running Zero latency app

Change-Id: Ib8a33b9e8dde3767337b9cd32c5b2849f9c8aa04
Reviewed-on: https://chromium-review.googlesource.com/823258
Commit-Ready: Gurchetan Singh <gurchetansingh@chromium.org>
Tested-by: Gurchetan Singh <gurchetansingh@chromium.org>
Reviewed-by: Gurchetan Singh <gurchetansingh@chromium.org>