ASoC: omap: fix compile-test building

The newly introduced driver causes a harmless Kconfig warning when
compile-testing random configurations:

WARNING: unmet direct dependencies detected for SND_SDMA_SOC
  Depends on [n]: SOUND [=y] && !UML && SND [=y] && SND_SOC [=y] && DMA_OMAP [=n]
  Selected by [y]:
  - SND_OMAP_SOC [=y] && SOUND [=y] && !UML && SND [=y] && SND_SOC [=y] && (ARCH_OMAP [=y] && DMA_OMAP [=n] || ARM [=y] && COMPILE_TEST [=y])

By simply allow build testing without DMA_OMAP, we can shut up that warning.

Fixes: dde637f2 ("ASoC: omap: Introduce the generic_dmaengine_pcm based sdma-pcm")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Mark Brown <broonie@kernel.org>