ASoC: soc-core: add soc_rtd_free()

ASoC: soc-core: add soc_rtd_free()

It is easy to read code if it is cleanly using paired function/naming,
like start <-> stop, register <-> unregister, etc, etc.
But, current ALSA SoC code is very random, unbalance, not paired, etc.
It is easy to create bug at the such code, and it will be difficult to
debug.

soc_rtd_init() was soc_post_component_init(), but there was no
its paired soc_post_component_free(), but it is done at
soc_remove_link_dais().
This means it is difficult to find related code.

This patch adds soc_rtd_free() which is paired soc_rtd_init().
soc_rtd_xxx() will be more cleanuped in the future.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Link: https://lore.kernel.org/r/87tva87lby.wl-kuninori.morimoto.gx@renesas.com
Signed-off-by: Mark Brown <broonie@kernel.org>