net: lan743x: Restore SGMII CTRL register on resume

net: lan743x: Restore SGMII CTRL register on resume

SGMII_CTRL register, which specifies the active interface, was not
properly restored when resuming from suspend. This led to incorrect
interface selection after resume particularly in scenarios involving
the FPGA.

To fix this:
- Move the SGMII_CTRL setup out of the probe function.
- Initialize the register in the hardware initialization helper function,
which is called during both device initialization and resume.

This ensures the interface configuration is consistently restored after
suspend/resume cycles.

Fixes: a46d9d37c4f4f ("net: lan743x: Add support for SGMII interface")
Signed-off-by: Thangaraj Samynathan <thangaraj.s@microchip.com>
Link: https://patch.msgid.link/20250516035719.117960-1-thangaraj.s@microchip.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>