ALSA: hda - Allow forcibly enabling/disabling snoop

User can pass snoop option to enable/disable the snoop behavior, but
currently azx_check_snoop_available() always turns it off for some
devices.  For better debuggability, change the parameter as bint, and
allow user to enable/disable forcibly the snoop when specified via the
module option.

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