This patch supports some type of machine drivers that set 0 to mclk
when sound device goes to idle state. After applied this patch,
sysclk == 0 means there is no constraint of sound rate and other
values will set constraints which is derived by sysclk setting.

Original code refuses sysclk == 0 setting. But some boards and SoC
(such as RockPro64 and RockChip I2S) has connected SoC MCLK out to
ES8316 MCLK in. In this case, SoC side I2S will choose suitable
frequency of MCLK such as fs * mclk-fs when user starts playing or
capturing.

Bad scenario as follows (mclk-fs = 256):
  - Initialize sysclk by correct value (Ex. 12.288MHz)
    - ES8316 set constraints of PCM rate by sysclk
      48kHz (1/256), 32kHz (1/384), 30.720kHz (1/400),
      24kHz (1/512), 16kHz (1/768), 12kHz (1/1024)
  - Play 48kHz sound, it's acceptable
  - Sysclk is not changed

  - Play 32kHz sound, it's acceptable
  - Set sysclk by 8.192MHz (= fs * mclk-fs = 32k * 256)
    - ES8316 set constraints of PCM rate by sysclk
      32kHz (1/256), 21.33kHz (1/384), 20.48kHz (1/400),
      16kHz (1/512), 10.66kHz (1/768), 8kHz (1/1024)

  - Play 48kHz again, but it's NOT acceptable because constraints
    list does not allow 48kHz
Signed-off-by: Katsuhiro Suzuki <katsuhiro@katsuster.net>
Link: https://lore.kernel.org/r/20190907163653.9382-2-katsuhiro@katsuster.netSigned-off-by: Mark Brown <broonie@kernel.org>