net: fec: rename struct fec_devinfo fec_imx6x_info -> fec_imx6sx_info

net: fec: rename struct fec_devinfo fec_imx6x_info -> fec_imx6sx_info

In da722186f654 ("net: fec: set GPR bit on suspend by DT
configuration.") the platform_device_id fec_devtype::driver_data was
converted from holding the quirks to a pointing to struct fec_devinfo.

The struct fec_devinfo holding the information for the i.MX6SX was
named fec_imx6x_info.

Rename fec_imx6x_info to fec_imx6sx_info to align with the SoC's name.

Reviewed-by: Wei Fang <wei.fang@nxp.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Link: https://patch.msgid.link/20250618-fec-cleanups-v4-5-c16f9a1af124@pengutronix.de
Signed-off-by: Jakub Kicinski <kuba@kernel.org>