The current clock registration and protection code has a few drawbacks, the
two main ones being that we create a lot of orphans clock in the
registration phase, which will be troublesome when we will start being less
relaxed about them.

The protection code also relies on clkdev, which we don't really use but
for this particular case.

Fix both at the same time by moving everyone to the CLK_OF_DECLARE that
will probe our clock tree in the right and thus avoid orphans, and by
protecting directly the clock returned by our registration function.
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>