[ARM] pxa: add namespace on ssp

In order to prevent code ambiguous, add namespace on functions in ssp driver.

Signed-off-by: Haojian Zhuang <haojian.zhuang@marvell.com>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Eric Miao <eric.y.miao@gmail.com>