phy: cadence: salvo: add .set_mode API

phy: cadence: salvo: add .set_mode API

For NXP platform design, the PHY can't know VBUS well, it causes the FSM
in controller seeing the disconnection at L1 use case. With .set_mode API
introduced, the controller driver could force PHY seeing B Session VALID
when it is at the device mode (VBUS is there), and keep FSM working well.

Signed-off-by: Peter Chen <peter.chen@nxp.com>
Signed-off-by: Frank Li <Frank.Li@nxp.com>
Link: https://lore.kernel.org/r/20230517161646.3418250-5-Frank.Li@nxp.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>