ATA: SATA_MV: Add missing Kconfig select statememnt

SATA_MV depends on GENERIC_PHY. So if SATA_MV is built in, GENERIC_PHY
cannot be modular. Fixes build error found by kbuild test robot.

Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Tejun Heo <tj@kernel.org>