ASoC: Explicitly say if we're powering up or down

Rather than passing the sequence to use for DAPM widgets around by reference
explicitly say if we're powering up or down until the point where we need
the sequence itself. This should make no practical difference in itself but
supports future refactoring.

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