ASoC: bcm: Remove obsoleted Kconfig dependency

CONFIG_SND_SOC_DMAENGINE_PCM was renamed to CONFIG_SND_DMAENGINE_PCM
recently.  And yet we don't have to select it since
CONFIG_SND_GENERIC_DMAENGINE_PCM selects the dependency by itself, so
just rip it off.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Acked-by: Florian Meier <florian.meier@koalo.de>
Signed-off-by: Mark Brown <broonie@linaro.org>