Follow the example of the rest of the QMP PHY drivers and move SGMII PCS
registers to a separate header file.

Cc: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20240126-phy-qmp-merge-common-v2-8-a463d0b57836@linaro.orgSigned-off-by: Vinod Koul <vkoul@kernel.org>