serial: sirf: use PM macro initialize PM functions

use SET_SYSTEM_SLEEP_PM_OPS to initialize suspend/resume functions
instead of legacy suspend and resume entries of platform_driver.
this will add hibernation support automatically as suspend to disk
entries are also set.

Signed-off-by: Qipan Li <Qipan.Li@csr.com>
Signed-off-by: Barry Song <Baohua.Song@csr.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>