This patch adds delay PHY power change from P0 to P1/P2/P3 when link state
changing from U0 to U1/U2/U3 respectively, and some special platforms can
configure that if it is needed.

[ balbi@ti.com : added DeviceTree binding documentation ]
Signed-off-by: Huang Rui <ray.huang@amd.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>