ASoC: rsnd: merge .nolock_start and .prepare

Main purpose of .nolock_start is we need to call
some function without spinlock.
OTOH we have .prepare which main purpose is
called under atomic context.
Then, it is called without spinlock.

In summary, our main callback init/quit, and start/stop
are called under "atomic context and with spinlock".
And some function need to be called under
"non-atomic context or without spinlock".
Let's merge .nolock_start and prepare to be more clear code.
Then, let's rename nolock_stop to cleanup

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Tested-by: Hiroyuki Yokoyama <hiroyuki.yokoyama.vx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>