ALSA: bebob: Add support for Focusrite Saffire/SaffirePro series

This commit allows this driver to support all of models which Focusrite
produces with DM1000/BeBoB. They are:
 - Saffire
 - Saffire LE
 - SaffirePro 10 I/O
 - SaffirePro 26 I/O

This commit adds Focusrite specific operations:
1. Get source of clock
2. Get/Set sampling frequency
3. Get metering information

The driver uses these functionalities to read/write specific address by async
transaction.

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>