PCI: dw-rockchip: Change get_ltssm() to provide L1 Substates info

PCI: dw-rockchip: Change get_ltssm() to provide L1 Substates info

Rename rockchip_pcie_get_ltssm() to rockchip_pcie_get_ltssm_reg() and add
rockchip_pcie_get_ltssm() to get_ltssm() callback in order to show the
proper L1 Substates. The PCIE_CLIENT_LTSSM_STATUS[5:0] register returns
the same LTSSM layout as enum dw_pcie_ltssm. So the driver just need to
convey L1 PM Substates by returning the proper value defined in
pcie-designware.h.

  cat /sys/kernel/debug/dwc_pcie_a40000000.pcie/ltssm_status
  L1_2 (0x142)

Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Link: https://patch.msgid.link/1765503205-22184-2-git-send-email-shawn.lin@rock-chips.com