pinctrl: sirf: add usp0_uart_nostreamctrl pin group for usp-uart without flowctrl

this patch adds the lost pin group which supports to let USP0 to simulate
a UART without hardware flow control.

Signed-off-by: Qipan Li <Qipan.Li@csr.com>
Signed-off-by: Barry Song <Baohua.Song@csr.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>