PCI: apple: Add driver for the Apple M1

Add a driver for the PCIe controller found in Apple system-on-chips,
particularly the Apple M1. This driver exposes the internal bus used for
the USB type-A ports, Ethernet, Wi-Fi, and Bluetooth. This patch brings
up the USB type-A ports and Ethernet. Bringing up the radios requires
interfacing with the System Management Coprocessor via Apple's
mailboxes, so that's left to a future patch.

In this state, the driver consists of two major parts: hardware
initialization and MSI handling. The hardware initialization is derived
from Mark Kettenis's U-Boot patches which in turn is derived from
Corellium's patches for the hardware. The rest of the driver is derived
from Marc Zyngier's driver for the hardware.

Co-developed-by: Stan Skowronek <stan@corellium.com>
Signed-off-by: Stan Skowronek <stan@corellium.com>
Co-developed-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>

MAINTAINERS

@@ -1274,6 +1274,7 @@ M:	Alyssa Rosenzweig <alyssa@rosenzweig.io>
 L:	linux-pci@vger.kernel.org
 S:	Maintained
 F:	Documentation/devicetree/bindings/pci/apple,pcie.yaml
+F:	drivers/pci/controller/pcie-apple.c
 
 APPLE SMC DRIVER
 M:	Henrik Rydberg <rydberg@bitmath.org>

drivers/pci/controller/Kconfig

@@ -312,6 +312,19 @@ config PCIE_HISI_ERR
 	  Say Y here if you want error handling support
 	  for the PCIe controller's errors on HiSilicon HIP SoCs
 
+config PCIE_APPLE
+	tristate "Apple PCIe controller"
+	depends on ARCH_APPLE || COMPILE_TEST
+	depends on OF
+	depends on PCI_MSI_IRQ_DOMAIN
+	depends on GPIOLIB
+	help
+	  Say Y here if you want to enable PCIe controller support on Apple
+	  system-on-chips, like the Apple M1. This is required for the USB
+	  type-A ports, Ethernet, Wi-Fi, and Bluetooth.
+
+	  If unsure, say Y if you have an Apple Silicon system.
+
 source "drivers/pci/controller/dwc/Kconfig"
 source "drivers/pci/controller/mobiveil/Kconfig"
 source "drivers/pci/controller/cadence/Kconfig"

drivers/pci/controller/Makefile

@@ -37,6 +37,7 @@ obj-$(CONFIG_VMD) += vmd.o
 obj-$(CONFIG_PCIE_BRCMSTB) += pcie-brcmstb.o
 obj-$(CONFIG_PCI_LOONGSON) += pci-loongson.o
 obj-$(CONFIG_PCIE_HISI_ERR) += pcie-hisi-error.o
+obj-$(CONFIG_PCIE_APPLE) += pcie-apple.o
 # pcie-hisi.o quirks are needed even without CONFIG_PCIE_DW
 obj-y				+= dwc/
 obj-y				+= mobiveil/