ARM: dts: sirf: add pin group for USP0 with only RX or TX frame sync for atlas6

add pin groups for USP0 only holding one of TX and RX frame sync. this patch
matches with the change in drivers/pinctrl/sirf.

commit 73f68c01 did this for prima2, but missed prima2. this patch fixes
the problem.

Signed-off-by: Rongjun Ying <rongjun.ying@csr.com>
Signed-off-by: Barry Song <Baohua.Song@csr.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>