net: pcs: xpcs: re-initiate clause 37 Auto-negotiation

net: pcs: xpcs: re-initiate clause 37 Auto-negotiation

The xpcs_switch_interface_mode function was introduced to handle
interface switching.

According to the XPCS datasheet, a soft reset is required to initiate
Clause 37 auto-negotiation when the XPCS switches interface modes.

When the interface mode switches from 2500BASE-X to SGMII,
re-initiating Clause 37 auto-negotiation is required for the SGMII
interface mode to function properly.

Signed-off-by: Choong Yong Liang <yong.liang.choong@linux.intel.com>
Link: https://patch.msgid.link/20250227121522.1802832-3-yong.liang.choong@linux.intel.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>