USB: DWC3: Generate interrupt on each TRB as default option

Currently in case of isoc, interrupt is programmed after each
TRB_NUM/4 ie 8th TRB. A TRB is programmed against each submitted
request from gadget. If we do not want to limit the minimum number of
necessary request to be submitted from gadget then we must receive
interrupt on each TRB submission. There can be such situation with a
gadget working with ping-pong buffer.

If a gadget does not want to receive interrupt after each request
completion then it may set no_interrupt flag.

Signed-off-by: Pratyush Anand <pratyush.anand@st.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>