dwc3: gadget: Use TXFIFO register based on used dwc3 version

TXFIFO register's bit(15) is reserved on usb31 version. Hence this
change starts using dwc3 version based TXFIFO size related macro
to update TXFIFO register while resizing TXFIFO of USB endpoint.

Change-Id: I1b9fb9d109f1ad8e1fd4bc23c75341bdec912c10
Signed-off-by: Mayank Rana <mrana@codeaurora.org>