phy: qcom: qmp-pcie: Add PHY register retention support

phy: qcom: qmp-pcie: Add PHY register retention support

Some QCOM PCIe PHYs support no_csr reset. Unlike BCR reset which resets the
whole PHY (hardware and register), no_csr reset only resets PHY hardware
but retains register values, which means PHY setting can be skipped during
PHY init if PCIe link is enabled in bootloader and only no_csr is toggled
after that.

Hence, determine whether the PHY has been enabled in bootloader by
verifying QPHY_START_CTRL register. If it's programmed and no_csr reset is
available, skip BCR reset and PHY register setting to establish the PCIe
link with bootloader - programmed PHY settings.

Signed-off-by: Qiang Yu <quic_qianyu@quicinc.com>
Signed-off-by: Wenbin Yao <quic_wenbyao@quicinc.com>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Tested-by: Aleksandrs Vinarskis <alex.vinarskis@gmail.com>
Link: https://lore.kernel.org/r/20250411113120.651363-3-quic_wenbyao@quicinc.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>