regulator: Don't increment use_count for boot_on regulators

Don't set use_count for regulators that are enabled at boot since this
stops the supply being disabled by well-behaved consumers which do
balanced enables and disabled. Any consumers which don't do disables
which are not matched by enables are unable to share regulators - shared
regulators are the common case so the API should facilitate them.

Consumers that want to disable regulators that are enabled when they
start have two options:

 - Do a regulator_enable() prior to the disable to bring the use count
   in sync with the hardware state; this will ensure that if the
   regulator was enabled by another driver then this consumer will play
   nicely with it.
 - Use regulator_force_disable(); this explicitly bypasses any checks
   done by the core and documents the inability of the driver to share
   the supply.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Liam Girdwood <lrg@slimlogic.co.uk>