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

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

Signed-off-by: Rongjun Ying <Rongjun.Ying@csr.com>
Signed-off-by: Barry Song <Barry.Song@csr.com>