This allows us to better detect whether a clk is enabled or not.

- If we can ask a clk, ask it. If it's enabled, go on and ask parents
- If we can't ask it, but it can be enabled, depend on the enable_count.
  if it's positive, go on and ask parents
- If we can't ask it and it cannot be enabled, assume it is enabled
  and ask parents.

This makes the CLK_ALWAYS_ENABLED unnecessary, since the fixed clk now
always returns 1 in its is_enabled callback.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>