PCI: imx6: Fix suspend/resume support on i.MX6QDL

In the Linux kernel, the following vulnerability has been resolved:

PCI: imx6: Fix suspend/resume support on i.MX6QDL

The suspend/resume functionality is currently broken on the i.MX6QDL
platform, as documented in the NXP errata (ERR005723):

https://www.nxp.com/docs/en/errata/IMX6DQCE.pdf

This patch addresses the issue by sharing most of the suspend/resume
sequences used by other i.MX devices, while avoiding modifications to
critical registers that disrupt the PCIe functionality. It targets the
same problem as the following downstream commit:

https://github.com/nxp-imx/linux-imx/commit/4e92355e1f79d225ea842511fcfd42b343b32995

Unlike the downstream commit, this patch also resets the connected PCIe
device if possible. Without this reset, certain drivers, such as ath10k
or iwlwifi, will crash on resume. The device reset is also done by the
driver on other i.MX platforms, making this patch consistent with
existing practices.

Upon resuming, the kernel will hang and display an error. Here's an
example of the error encountered with the ath10k driver:

ath10k_pci 0000:01:00.0: Unable to change power state from D3hot to D0, device inaccessible
Unhandled fault: imprecise external abort (0x1406) at 0x0106f944

Without this patch, suspend/resume will fail on i.MX6QDL devices if a
PCIe device is connected.

[kwilczynski: commit log, added tag for stable releases]