phy: cadence: salvo: add access for USB2PHY

There is an offset for USB2PHY in SALVO phy, add offset parameter for read
and write API to cover both USB2 and USB3 PHY control.

Signed-off-by: Peter Chen <peter.chen@nxp.com>
Signed-off-by: Frank Li <Frank.Li@nxp.com>
Link: https://lore.kernel.org/r/20230517161646.3418250-2-Frank.Li@nxp.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>