MatrixFree setup of face data: Set up what the user requests

[kronbichler]

In the setup of MatrixFree with faces enabled, we currently set up both the inner faces and the boundary faces if the user requests either of the two. We should fix this, so that eventually only the things that were actually requested get constructed. The most pressing case is that a user only requested boundary faces, but got inner faces and some slowdown in the ghost exchange induced by the possible need to resolve the dependencies for face integrals. See #12762 (review) for a current confusion.