PCI: rockchip: Disable RC's ASPM L0s based on DT "aspm-no-l0s"

Rockchip's RC produces a 100MHz reference clock but there are two methods
for the PHY to generate it:

  (1) Use the system PLL to generate a 100MHz clock.  The PHY will relock
      it, filter signal noise, and output the reference clock.  ASPM L0s
      works correctly, but circuit noise issues make it difficult to pass
      the TX compatibility test.

  (2) Share the SoC's 24MHZ crystal oscillator with the PHY and force the
      PHY's PLL to generate 100MHz internally.  In this case, exit from
      ASPM L0s sometimes fails due to a design error in the RC receiver
      circuit.  Even if we use extended-synch, the PHY sometimes fails to
      relock the bits from FTS, which will hang the system.

We want the flexibility to use both clocking methods, so add a DT property,
"aspm-no-l0s".  If that's present, disable L0s to avoid the issues with
case (2).

[bhelgaas: changelog]
Reported-by: Jeffy Chen <jeffy.chen@rock-chips.com>
Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Brian Norris <briannorris@chromium.org>
Acked-by: Rob Herring <robh@kernel.org>