irqchip: Renesas INTC External IRQ pin driver

irqchip: Renesas INTC External IRQ pin driver

This patch adds a driver for external IRQ pins connected
to the INTC block on recent SoCs from Renesas.

The INTC hardware block usually contains a rather wide
range of features ranging from external IRQ pin handling
to legacy interrupt controller support. On older SoCs
the INTC is used as a general purpose interrupt controller
both for external IRQ pins and on-chip devices.

On more recent ARM based SoCs with Cortex-A9 the main
interrupt controller is the GIC, but IRQ trigger setup
still need to happen in the INTC hardware block.

This driver implements the glue code needed to configure
IRQ trigger and also handle mask/unmask and demux of
external IRQ pins hooked up from the INTC to the GIC.

Tested on sh73a0 and r8a7779. The hardware varies quite
a bit with SoC model, for instance register width and
bitfield widths vary wildly. The driver requires one GIC
SPI per external IRQ pin to operate.  Each driver instance
will handle up to 8 external IRQ pins.

The SoCs using this driver are currently mainly used
together with regular platform devices so this driver
allows configuration via platform data to support things
like static interrupt base address. DT support will
be added incrementally in the not so distant future.

Signed-off-by: Magnus Damm <damm@opensource.se>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>