PCI: kirin: Support PERST# GPIOs for HiKey970 external PEX 8606 bridge

PCI: kirin: Support PERST# GPIOs for HiKey970 external PEX 8606 bridge

On HiKey970, there's a PEX 8606 PCI bridge on its PHY with 6 lanes. Only 4
lanes are connected:

  lane 0 - connected to Kirin 970 (upstream)
  lane 4 - M.2 slot
  lane 5 - mini PCIe slot
  lane 6 - on-board Ethernet controller

Each lane has its own PERST# GPIO pin and needs a clock request.

Add support to parse a DT schema containing the above data.

HiKey 970 requires a little more waiting time for the PCI bridge - which is
outside the SoC - to finish the PERST# reset, and then initialize the eye
diagram.

Increase the waiting time for the PERST# signals accordingly.

[bhelgaas: squash refcount fix from Wan Jiabing <wanjiabing@vivo.com>:
https://lore.kernel.org/r/20211103062518.25695-1-wanjiabing@vivo.com
and drop "parent" refcount per
https://lore.kernel.org/all/20211103143059.GA683503@bhelgaas/]
Link: https://lore.kernel.org/r/bb391a0e0f0863b66e645048315fab1a4f63f277.1634812676.git.mchehab+huawei@kernel.org
Link: https://lore.kernel.org/all/9a365cffe5af9ec5a1f79638968c3a2efa979b65.1634622716.git.mchehab+huawei@kernel.org/
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Xiaowei Song <songxiaowei@hisilicon.com>
Cc: Kishon Vijay Abraham I <kishon@ti.com>