phy: miphy28lp: Add SSC support for SATA

This patch to tune on/off the ssc on miphy sata setup.
User can now enable ssc via dt blob, it is useful to reduce
effects of EMI.

Signed-off-by: Giuseppe Condorelli <giuseppe.condorelli@st.com>
Signed-off-by: Gabriel Fernandez <gabriel.fernandez@linaro.org>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>