ALSA: PCM midlevel: introduce mask for xrun_debug() macro

For debugging purposes, it is better to separate actions.

Bit-values:

	1: show bad PCM ring buffer pointer
	2: show also stack (to debug kernel latency issues)
	4: check pointer against system jiffies

Example:

	5: show bad PCM ring buffer pointer and do jiffies check

Signed-off-by: Jaroslav Kysela <perex@perex.cz>
Signed-off-by: Takashi Iwai <tiwai@suse.de>