phy: fsl-imx8mp-usb: add support for phy tuning

Add USB PHY parameter tuning for USB certifications.

Reviewed-by: Haibo Chen <haibo.chen@nxp.com>
Signed-off-by: Li Jun <jun.li@nxp.com>
[j.zink: ported to v6.3-rc1 from NXP downstream repo + cleanups]
Signed-off-by: Johannes Zink <j.zink@pengutronix.de>
Link: https://lore.kernel.org/r/20230516-lustige-usb-phy-dinge-v2-2-3383a0de34ac@pengutronix.de
Signed-off-by: Vinod Koul <vkoul@kernel.org>