ALSA: hda - Update documentation

Update documentation regarding codec probing; the new probe_only option
and the new probe_mask usage.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/Documentation/sound/alsa/ALSA-Configuration.txt b/Documentation/sound/alsa/ALSA-Configuration.txt
index 841a936..012afd7 100644
--- a/Documentation/sound/alsa/ALSA-Configuration.txt
+++ b/Documentation/sound/alsa/ALSA-Configuration.txt
@@ -757,6 +757,9 @@
     model	- force the model name
     position_fix - Fix DMA pointer (0 = auto, 1 = use LPIB, 2 = POSBUF)
     probe_mask  - Bitmask to probe codecs (default = -1, meaning all slots)
+    		  When the bit 8 (0x100) is set, the lower 8 bits are used
+		  as the "fixed" codec slots; i.e. the driver probes the
+		  slots regardless what hardware reports back
     probe_only	- Only probing and no codec initialization (default=off);
 		  Useful to check the initial codec status for debugging
     bdl_pos_adj	- Specifies the DMA IRQ timing delay in samples.