ASoC: soc-dapm: add snd_soc_dapm_alloc()

ASoC: soc-dapm: add snd_soc_dapm_alloc()

Because struct snd_soc_dapm_context is soc-dapm framework specific, user
driver don't need to access its member directly, we would like to hide
them. struct snd_soc_dapm_context will be removed from header in the
future.

Current card/component are using dapm_context instance. But it will be
moved to soc-dapm.c, and we can use will be only pointer. Makes it to
pointer.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Link: https://patch.msgid.link/87h5shqgw1.wl-kuninori.morimoto.gx@renesas.com
Signed-off-by: Mark Brown <broonie@kernel.org>