PCI: dwc: exynos: Rework the driver to support Exynos5433 variant

Exynos5440 SoC support has been dropped since commit 8c83315 ("ARM:
dts: exynos: Remove Exynos5440"). Rework this driver to support DWC PCIe
variant found in the Exynos5433 SoCs.

The main difference in Exynos5433 variant is lack of the MSI support
(the MSI interrupt is not even routed to the CPU).

[mszyprow: reworked the driver to support only Exynos5433 variant,
	   simplified code, rebased onto current kernel code, added
	   regulator support, converted to the regular platform driver,
	   removed MSI related code, rewrote commit message, added help]

Link: https://lore.kernel.org/r/20201113170139.29956-6-m.szyprowski@samsung.com
Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Jingoo Han <jingoohan1@gmail.com>

drivers/pci/controller/dwc/Kconfig

@@ -83,10 +83,15 @@ config PCIE_DW_PLAT_EP
 	  selected.
 
 config PCI_EXYNOS
-	bool "Samsung Exynos PCIe controller"
-	depends on SOC_EXYNOS5440 || COMPILE_TEST
+	tristate "Samsung Exynos PCIe controller"
+	depends on ARCH_EXYNOS || COMPILE_TEST
 	depends on PCI_MSI_IRQ_DOMAIN
 	select PCIE_DW_HOST
+	help
+	  Enables support for the PCIe controller in the Samsung Exynos SoCs
+	  to work in host mode. The PCI controller is based on the DesignWare
+	  hardware and therefore the driver re-uses the DesignWare core
+	  functions to implement the driver.
 
 config PCI_IMX6
 	bool "Freescale i.MX6/7/8 PCIe controller"