uinput: add Ravenwood test target

The unit tests for the uinput command don't currently use any Android
APIs, but can't be run on the host. Add a Ravenwood test target so that
they can.

Test: $ atest --host UinputTestsRavenwood
Bug: 245989146
Flag: TEST_ONLY
Change-Id: I150efac6e6d1fff83a48f0ad7d895d315fb736de