phy: miphy28lp: Provide support for the MiPHY28lp Generic PHY

The MiPHY28lp is a Generic PHY which can serve various SATA or PCIe
or USB3 devices.

Signed-off-by: alexandre torgue <alexandre.torgue@st.com>
Signed-off-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Signed-off-by: Gabriel Fernandez <gabriel.fernandez@linaro.org>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>