minigbm: allow for multiple {format, modifier} pairs in combination list

minigbm: allow for multiple {format, modifier} pairs in combination list

With CL:405019, drv_insert_supported_combination appended flags if the
{format, modifier} pair was already in the list. This would result
in the BO_USE_RENDERING flag being in the same supported combination
as BO_USE_LINEAR, even though the arrays in the drivers try to separate
these cases. Initially, add all the combinations specified by
the drivers. When querying KMS, add a helper function that modifies
existing combinations if they already exist.

BUG=b:31942635,
TEST=graphics_Gbm, Chrome boots on minnie
CQ-DEPEND=CL:414584

Change-Id: I64326be2078ae745fca2c819e8344797aef3c667
Reviewed-on: https://chromium-review.googlesource.com/415442
Commit-Ready: Gurchetan Singh <gurchetansingh@chromium.org>
Tested-by: Gurchetan Singh <gurchetansingh@chromium.org>
Reviewed-by: Stéphane Marchesin <marcheu@chromium.org>