pci: Add DW PCIe controller support for iMX8MP SoC

pci: Add DW PCIe controller support for iMX8MP SoC

pcie_imx doesn't seem to share any useful code for iMX8 SoC and it is
tied to quite old port of pcie_designware driver from Linux which
suffices only iMX6 specific needs.

But currently we have the common DWC specific bits which alligns pretty
well with DW PCIe controller on iMX8MP SoC. So lets reuse those common
bits instead as a new driver for iMX8 SoCs. It should be fairly easy to
add support for other iMX8 variants to this driver.

iMX8MP SoC also comes up with standalone PCIe PHY support, so hence we
can reuse the generic PHY infrastructure to power on PCIe PHY.

Tested-by: Tim Harvey <tharvey@gateworks.com> #imx8mp-venice*
Tested-by: Adam Ford <aford173@gmail.com> #imx8mp-beacon-kit
Reviewed-by: Marek Vasut <marex@denx.de>
Signed-off-by: Sumit Garg <sumit.garg@linaro.org>