usb: gadget: u_ether: Add module param to config cpu boost freq

commit:05112982 "usb: gadget: u_ether: add scatter/gather support"
hard codes boost the cpus to 1Ghz. This will not work for all
plaforms as they may not support this frequency. Add module param
to let different platoforms configure cpu boost frequency when usb
ethernet interface is active.

Change-Id: Ieb7e8016f201637bc050752738c35aba86b45228
Signed-off-by: Vamsi Krishna <vskrishn@codeaurora.org>