MLK-10203-1 pci: imx: enable imx6qdl pcie support

MLK-10203-1 pci: imx: enable imx6qdl pcie support

enable imx6qdl pcie on imx_3.14 kernel
and add the pcie pm workaround for imx6qdl.
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L2 can exit by 'reset' or Inband beacon (from remote EP)
toggling phy_powerdown has same effect as 'inband beacon'
So, toggle bit18 of GPR1, used as a workaround of errata
"PCIe PCIe does not support L2 Power Down"
WARNING: This is not official workaround for ERR005723.
Fortunately, we don't encounter issue with this workaround.
User should take own risk to use it.

Signed-off-by: Richard Zhu <Richard.Zhu@freescale.com>
(cherry picked from commit 4cdd4fb7fb3b3e746b66838f4cdd24fccd67c78d)