gpio: thunderx: Switch to GPIOLIB_IRQCHIP

Use the new infrastructure for hierarchical irqchips in
gpiolib.

The major part of the rewrite was dues to the fact that
the driver was passing around a per-irq pointer to
struct thunderx_line * data container, and the central
handlers will assume struct gpio_chip * to be passed
to we need to use the hwirq as index to look up the
struct thunderx_line * for each IRQ.

The pushing and pop:ing of the irqdomain was confusing
because I've never seen this before, but I tried to
replicate it as best I could.

I have no chance to test or debug this so I need
help.

Cc: David Daney <david.daney@cavium.com>
Cc: Thierry Reding <treding@nvidia.com>
Cc: Brian Masney <masneyb@onstation.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20190808123242.5359-4-linus.walleij@linaro.org

drivers/gpio/Kconfig

@@ -539,6 +539,7 @@ config GPIO_THUNDERX
 	tristate "Cavium ThunderX/OCTEON-TX GPIO"
 	depends on ARCH_THUNDER || (64BIT && COMPILE_TEST)
 	depends on PCI_MSI
+	select GPIOLIB_IRQCHIP
 	select IRQ_DOMAIN_HIERARCHY
 	select IRQ_FASTEOI_HIERARCHY_HANDLERS
 	help