crosvm: Add USE flag to enable gpu feature.

BUG=chromium:837073
TEST=USE="crosvm-gpu" emerge-$BOARD crosvm

Change-Id: I66750d3a8f3353e57e3234841a42ea6662e6879f
Reviewed-on: https://chromium-review.googlesource.com/1184215
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: David Riley <davidriley@chromium.org>
Reviewed-by: Chirantan Ekbote <chirantan@chromium.org>
1 file changed