Alsa driver finalization

I think the alsa sound driver is now in a pretty acceptable state for the next release. I did some cleanup / renaming and introduced a module parameter for the maximal samplerate (_maxSampleRate_, default is 22050).

In order to reduce the clicks when turning the amp on/off, I've implemented a ramping from 0 to 50% PWM duty. One can configure the ramp time with the module parameter _rampMS_ (default 20 ms).

Additionally, I've added a module parameter _debug_ who enables some _printk_ logging if set to 'Y' (default is off).

Please find here a sample _modprobe.d_ file for configuring the driver:
<pre><code>#file /etc/modprobe.d/legoev3-snd.conf
#options snd_legoev3 maxSampleRate=48000
#options snd_legoev3 rampMS=30
#options snd_legoev3 debug=Y
</code></pre>