CRAS: mix - Short circuit some scaling.

Add checks if it is worth scaling before doing the scaling.
Re-order cras_mix add to be more readable and take advantage of the
new check in scale_add_clip.

Change-Id: I4a4f340e13f4167e57ff83429b2eea33519751aa
Signed-off-by: Dylan Reid <dgreid@chromium.org>
CRAS: mix - reorder exported functions

This will make it clearer when the scale and mix_add functions expand
to support formats other than s16le.

Change-Id: I28c6403e2c35d93164b8c6ea6dc758994bac1e81
Signed-off-by: Dylan Reid <dgreid@chromium.org>
CRAS: mix - Pass format in to functions that will need it

To allow cras_mix to mix and scale formats othedr than s16_le, pass
that format in as an argument.

Change-Id: Iaf5e25c9a1653ed1b4c9b1b39fead9c5dc8005fc
Signed-off-by: Dylan Reid <dgreid@chromium.org>