phy: qcom-sgmii-eth: use PHY interface mode for SerDes settings

phy: qcom-sgmii-eth: use PHY interface mode for SerDes settings

As established in the previous commit, using SPEED_1000 and SPEED_2500
does not make sense for a SerDes due to the PCS encoding that is used
over the SerDes link, which inflates the data rate at the SerDes. Thus,
the use of these constants in a SerDes driver is incorrect.

Since qcom-sgmii-eth no longer implements phy_set_speed(), but instead
uses the PHY interface mode passed via the .set_mode() method, convert
the driver to use the PHY interface mode internally to decide whether
to configure the SerDes for 1.25Gbps or 3.125Gbps mode.

Tested-by: Mohd Ayaan Anwar <mohd.anwar@oss.qualcomm.com>
Acked-by: Vinod Koul <vkoul@kernel.org>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/E1vxS4E-0000000BQXg-46dJ@rmk-PC.armlinux.org.uk
Signed-off-by: Jakub Kicinski <kuba@kernel.org>