drivers: add ufs stack ...

If UFS device is initialized, we could just make it out of
hibernation by UFS_FLAGS_SKIPINIT. And vendor's dirver is always
focus on PHY setting. We could use UFS driver directly if it
exits from hibernation.

There're eight LUNs in UFS device. The UFS driver only provides
the read/write API with LUN. User could define his own read/write
since user may want to access different LUNs.

Signed-off-by: Haojian Zhuang <haojian.zhuang@linaro.org>