bebob: re-arrangement for model specific operations

BeBoB chipset can be customized validly. But I believe the codes should be in
user land, not in kernel land as much as possible.

This commit reduce dig_iface opetation and arrange sampling frequency and
clock source.

M-Audio Firewire 1814 and ProjectMix I/O is a special customized version of
Bebob and there is 'write-only' settings. The controls should be in kernel
land.