Previously, descriptors of the test devices were stored direclty in the mock
device files (e.g., "mock_[hid|msc].[h|c]"). This commit splits out the device
descriptors to separate files (e.g., "dev_[hid|msc].c") along with getter
functions.
Users that want to run the tests locally on a different device simply need to
update the "dev_[hid|msc].c" file for their device.
