phy: add a driver for the Berlin SATA PHY

The Berlin SoC has a two SATA ports. Add a PHY driver to handle them.

The mode selection can let us think this PHY can be configured to fit
other purposes. But there are reasons to think the SATA mode will be
the only one usable: the PHY registers are only accessible indirectly
through two registers in the SATA range, the PHY seems to be integrated
and no information tells us the contrary. For these reasons, make the
driver a SATA PHY driver.

Signed-off-by: Antoine Ténart <antoine.tenart@free-electrons.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>