dwc3: Preserve TxFIFO of IN/INT EP for UDC without tx-fifo-resize

We are clearing existing allocated TxFIFO during set_config
even if a controller does not have tx-fifo-resize flag set
in the DT. Also we do not resize the FIFOs for such controller.
As a result, the FIFO depths for the IN/INT EPs (excpet 0 IN)
of the controller are 0 and it cannot work in device mode.

Fix this issue by not clearing the default TxFIFO if
tx-fifo-resize flag is not set.

Change-Id: I5cf7d2eb017b8ed55348e578c10856d62a3e282e
Signed-off-by: Ajay Agarwal <ajaya@codeaurora.org>