phy: miphy28lp: Tune tx impedance across Soc cuts

This patch to compensate tx impedance (Sata, PCIe)
depending on Soc cuts the kernel is built for.

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>