usb: dwc3: debug: Add dbg_log_string to log strings

Even though dwc3 logging uses ipc logging it still applies
restrictions with size and number parameters. Add additional
macro to log formatted strings.

Change-Id: Iee6dbec08d5cda1202c7261800b490bcb2b313fb
Signed-off-by: Vamsi Krishna Samavedam <vskrishn@codeaurora.org>