ALSA: doc: ReSTize writing-an-alsa-driver document

Another simple conversion from DocBook to ReST.
This required a few manual fixups and reformats, but the most of
contents are kept as is.
Signed-off-by: Takashi Iwai <tiwai@suse.de>

Documentation/DocBook/Makefile

@@ -12,8 +12,7 @@ DOCBOOKS := z8530book.xml  \
 	    kernel-api.xml filesystems.xml lsm.xml usb.xml kgdb.xml \
 	    gadget.xml libata.xml mtdnand.xml librs.xml rapidio.xml \
 	    genericirq.xml s390-drivers.xml uio-howto.xml scsi.xml \
-	    debugobjects.xml sh.xml regulator.xml \
-	    writing-an-alsa-driver.xml \
+	    80211.xml debugobjects.xml sh.xml regulator.xml \
 	    tracepoint.xml w1.xml \
 	    writing_musb_glue_layer.xml crypto-API.xml iio.xml
 

Documentation/sound/kernel-api/index.rst

@@ -5,3 +5,4 @@ ALSA Kernel API Documentation
    :maxdepth: 2
 
    alsa-driver-api
+   writing-an-alsa-driver