Add a library build rule for ml_service mojo files

This library build rule is needed in order for platform2/ml to
conveniently depend on & use these interfaces.

Converted the 'action' to a 'rule' in order to build our multiple
mojoms.

Also fixed some typos in the existing mojoms that didn't have a build
rule yet.

TEST=Used from an in-progress platform2/ml CL on my machine.
BUG=chromium:836091

Change-Id: Ia0b8ebffcfae3f5cd54599f89f0f24b466023335
Reviewed-on: https://chromium-review.googlesource.com/1032133
Commit-Ready: Andrew Moylan <amoylan@chromium.org>
Tested-by: Andrew Moylan <amoylan@chromium.org>
Reviewed-by: Eric Caruso <ejcaruso@chromium.org>
3 files changed