USB: ci13xxx: Remove support to enable function based streaming

USB streaming mode is now enabled by default which also bumps
up usb_core clock to max_nominal. Hence, remove deprecated
code to enable streaming mode based on function selected
and change usb core frequency between default and max_nominal
from udc driver.

Change-Id: I925d7d954bb20b8d8495bcf6a719568512b7d2fc
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>