regulator: core: Apply system load even if no consumer loads

Prior to commit 5451781d ("regulator: core: Only count load for
enabled consumers") we used to always add up the total load on every
enable in _regulator_enable().  After that commit we only updated the
total load when enabling / disabling a regulator where a consumer
specified a load or when changing the consumer load on an enabled
regulator.

The problem with the new scheme is that if there is a system load
specified for a regulator but no consumers specify a load then we
never account for it.

Let's account for the system load in set_machine_constraints().

NOTE: with the new scheme we end up with a bit of a quandry.  What if
someone specifies _both_ an initial mode and a system load?  If we
take the system load into account right at init time then it will
effectively clobber the initial mode.  We'll resolve this by saying
that if both are specified then the initial mode will win.  The system
load will then only take effect if/when a consumer specifies a load.
If no consumers ever specify a load then the initial mode will persist
and the system load will have no effect.

Fixes: 5451781d ("regulator: core: Only count load for enabled consumers")
Reported-by: Brian Masney <masneyb@onstation.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Tested-by: Brian Masney <masneyb@onstation.org>
Signed-off-by: Mark Brown <broonie@kernel.org>