ASoC: Add helper functions for deferred regmap setup

Some drivers (most notably the AC'97 drivers) do not have access to their
regmap struct when the component/codec is registered. For those drivers the
automatic regmap setup will not work and needs to be done manually,
typically from the component/CODEC drivers probe callback.

This patch adds a set of helper function to handle deferred regmap
initialization as well as early regmap tear-down.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@kernel.org>