sh: clkfwk: Tidy up on-chip clock registration and rate propagation.

This tidies up the set_rate hack that the on-chip clocks were abusing to
trigger rate propagation, which is now handled generically.

Additionally, now that CLK_ENABLE_ON_INIT is wired up where it needs to
be for these clocks, the clk_enable() can go away. In some cases this was
bumping up the refcount higher than it should have been.

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