ALSA: pcm: Fix sparse warnings wrt snd_pcm_state_t

Since we have a bitwise definition of snd_pcm_state_t and use it for
certain struct fields, a few new (and years old) sparse warnings came
up.  This patch is an attempt to cover them.

- The state fields in snd_pcm_mmap_status* and co are all defined as
  snd_pcm_state_t type now

- The PCM action callbacks take snd_pcm_state_t argument as well;
  some actions taking special values got the explicit cast and
  comments

- For the PCM action that doesn't need an extra argument receives
  ACTION_ARG_IGNORE instead of ambiguous 0

While we're at it, the boolean argument is also properly changed to
bool and true/false, as well as a slight refactoring of PCM pause
helper function to make easier to read.

No functional changes, just shutting up chatty sparse.

Fixes: 46b770f7 ("ALSA: uapi: Fix sparse warning")
Reported-by: kbuild test robot <lkp@intel.com>
Link: https://lore.kernel.org/r/20200131152214.11698-1-tiwai@suse.de


Signed-off-by: Takashi Iwai <tiwai@suse.de>