Improve recipe naming

The naming of the various toolchain component recipes was unduly
long, and similar names made it easy to get confused, and hard to
write short wildcards that matched the specific file you wanted.

Renaming:

    external-sourcery-* and external-sourcery-toolchain-*
    become sourcery-tc-*.

    eglibc-sourcery-prebuilt and eglibc-sourcery become
    eglibc-sourcery-binary and eglibc-sourcery-compile,
    respectively.

Signed-off-by: Peter Seebach <peter.seebach@windriver.com>