ALSA: usb-audio: Add resume support for Native Instruments controls

The changes at this time are a bit more wider than previous ones.
Firstly, the NI controls didn't cache the values, so I had to
implement the caching.  It's stored in bit 24 of private_value.
In addition to that, the initial values have to be read from
registers.

Signed-off-by: Takashi Iwai <tiwai@suse.de>