spi: sirf: use SET_SYSTEM_SLEEP_PM_OPS to initialize PM entries

use SET_SYSTEM_SLEEP_PM_OPS to initialize PM entries, this makes the codes
clean and also enable the ability of hibernation support for sirf SPI.

Signed-off-by: Qipan Li <Qipan.Li@csr.com>
Signed-off-by: Barry Song <Baohua.Song@csr.com>
Signed-off-by: Mark Brown <broonie@linaro.org>