sh: clkfwk: Kill off remaining debugfs cruft.

Now that all of the named string association with clocks has been
migrated to clkdev lookups there's no meaningful named topology that can
be constructed for a debugfs tree view. Get rid of the left over bits,
and shrink struct clk a bit in the process.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>