ASoC: pxa2xx-ac97: Remove unused DAI ID defines

The DAI ID defines are back from the time when DAIs were referenced by a
numerical ID. These days a string is used instead and the defines are
unused. The last user of these defines was removed in commit f0fba2ad
("ASoC: multi-component - ASoC Multi-Component Support"). So remove the
defines as well.

This also means the pxa2xx-ac97.h file no longer has any content and can be
removed.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Tested-by: Robert Jarzmik <robert.jarzmik@free.fr> (for mioa701_wm9713)
Signed-off-by: Mark Brown <broonie@kernel.org>