PCI: mediatek: Add controller support for MT2712 and MT7622

MT2712 and MT7622 using a new IP block of Gen2 controller which has two
root ports and shares the same probing flow with MT2701/MT7623.

Both MT2712 and MT7622 have the same per-port control registers, but
there are slight differences between them:

  - MT7622 has more clocks than MT2712.

  - MT7622 has shared control registers which are used to enable LTSSM and
    ASPM while MT2712 does not.

Add host controller support for MT2712/MT7622.

Signed-off-by: Ryder Lee <ryder.lee@mediatek.com>
Signed-off-by: Honghui Zhang <honghui.zhang@mediatek.com>
[bhelgaas: folded in fix from http://lkml.kernel.org/r/1502715868-17651-2-git-send-email-honghui.zhang@mediatek.com]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

drivers/pci/host/Kconfig

@@ -182,14 +182,13 @@ config PCIE_ROCKCHIP
 
 config PCIE_MEDIATEK
 	bool "MediaTek PCIe controller"
-	depends on ARM && (ARCH_MEDIATEK || COMPILE_TEST)
+	depends on (ARM || ARM64) && (ARCH_MEDIATEK || COMPILE_TEST)
 	depends on OF
 	depends on PCI
 	select PCIEPORTBUS
 	help
 	  Say Y here if you want to enable PCIe controller support on
-	  MT7623 series SoCs.  There is one single root complex with 3 root
-	  ports available.  Each port supports Gen2 lane x1.
+	  MediaTek SoCs.
 
 config PCIE_TANGO_SMP8759
 	bool "Tango SMP8759 PCIe controller (DANGEROUS)"