ozone: Add initial build support for xkbcommon

This adds a use_xkbcommon variable that allows usage of libxkbcommon in
the build. Turn this on for linux ozone builds (except embedded builds).

BUG=430194
TEST=build

Review URL: https://codereview.chromium.org/751623003

Cr-Commit-Position: refs/heads/master@{#308204}
4 files changed