drivers: sh: late disabling of clocks V2

This V2 patch changes the clock disabling behavior during boot.
Two different changes are made:

1) Delay disabling of clocks until late in the boot process.
   This fixes an existing issue where in-use clocks without
   software reference are disabled by mistake during boot.
   One example of this is the handling of the Mackerel serial
   console output that shares clock with the I2C controller.

2) Write out the "disabled" state to the hardware for clocks
   that not have been used by the kernel. In other words,
   make sure so far unused clocks actually get turned off.

Signed-off-by: Magnus Damm <damm@opensource.se>
Acked-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>