Rename mmp files to be predictable and intuitive

Rename mmp files to be predictable and intuitive to make it practical to use "sbs -p <subproject>.mmp -c armv6_urel" to build single subproject. Currently mmp filenames include UID, which is difficult to remember. Mmp filenames should use target binary name instead; it'll be just as unique as all binaries will end up in single directory anyway.