mfd: intel-ehl-gpio: Introduce MFD framework to PSE GPIO/TGPIO

In Elkhart Lake, the PSE GPIO and TGPIO shares the PCI device,
albeit being accessed at different MMIO BAR offset. Thus, to properly
register device drivers and enable support of both functionalities,
we choose Linux MFD framework.

1) intel-ehl-gpio - probe base on the PCI device, and split the resources
accordingly.
2) gpio-ehl-pse-plat - platform driver which will register support of
PSE GPIO (30 pins max per device)
3) ptp-intel-tgpio-plat - platform driver which will register support of
PSE TGPIO (20 pins max per device)

Note: BIOS configuration is required to properly assign the pin-mux.
Note: PSE TGPIO driver is based on Balbi Felipe's original driver.
Note: PSE GPIO driver is based on Pandith N's original driver.

Signed-off-by: N Pandith <pandith.n@intel.com>
Signed-off-by: Raymond Tan <raymond.tan@intel.com>

drivers/gpio/Kconfig

@@ -246,6 +246,17 @@ config GPIO_EM
 	help
 	  Say yes here to support GPIO on Renesas Emma Mobile SoCs.
 
+config GPIO_EHL_PSE_PLAT
+	tristate "Intel EHL PSE GPIO support as platform MFD"
+	depends on ACPI && X86
+	select GPIOLIB_IRQCHIP
+	help
+	  Enable Intel EHL PSE GPIO support as platform
+	  MFD.
+
+	  Driver for GPIO functionality on Intel Elkhart Lake SoC on
+	  PSE under Host-Owned mode.
+
 config GPIO_EP93XX
 	def_bool y
 	depends on ARCH_EP93XX

drivers/gpio/Makefile

@@ -80,6 +80,7 @@ obj-$(CONFIG_GPIO_LP873X)		+= gpio-lp873x.o
 obj-$(CONFIG_GPIO_LP87565)		+= gpio-lp87565.o
 obj-$(CONFIG_GPIO_LPC18XX)		+= gpio-lpc18xx.o
 obj-$(CONFIG_GPIO_LPC32XX)		+= gpio-lpc32xx.o
+obj-$(CONFIG_GPIO_EHL_PSE_PLAT)		+= gpio-ehl-pse-plat.o
 obj-$(CONFIG_GPIO_MADERA)		+= gpio-madera.o
 obj-$(CONFIG_GPIO_MAX3191X)		+= gpio-max3191x.o
 obj-$(CONFIG_GPIO_MAX7300)		+= gpio-max7300.o