usb: gadget: f_uac2: Support for multiple sample rates

Adds support for multiple sample rates by changing the
fixed clock sources to programmable clock sources.
The HOST can get the supported sample rates by sending
a GET RANGE request to the clock source and the HOST
can select a sample rate by sending a SET CUR request
targeted at the clock source with one of the supported
sample rates. Adds support for 44.1 kHz and 48 kHz.

Change-Id: Icc829abc39b3911975fe379545dff35ec2faf7d1
Signed-off-by: Sriharsha Allenki <sallenki@codeaurora.org>