phy: ti: gmii-sel: Enable USXGMII mode for J784S4

TI's J784S4 SoC supports USXGMII mode with the CPSW9G instance's MAC
ports 1 and 2. Add USXGMII mode to the extra_modes member of J784S4's
SoC data.

Signed-off-by: Siddharth Vadapalli <s-vadapalli@ti.com>
Reviewed-by: Roger Quadros <rogerq@kernel.org>
Link: https://lore.kernel.org/r/20230331062521.529005-3-s-vadapalli@ti.com


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