phy: qcom-qmp-pcie: clean up power-down handling

Always define the POWER_DOWN_CONTROL register instead of falling back to
the v2 offset during power on and power off.

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Johan Hovold <johan+linaro@kernel.org>
Link: https://lore.kernel.org/r/20221017065013.19647-5-johan+linaro@kernel.org


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