irqchip: Add driver for WPCM450 interrupt controller

irqchip: Add driver for WPCM450 interrupt controller

The WPCM450 AIC ("Advanced Interrupt Controller") is the interrupt
controller found in the Nuvoton WPCM450 SoC and other Winbond/Nuvoton
SoCs.

The list of registers if based on the AMI vendor kernel and the
Nuvoton W90N745 datasheet.

Although the hardware supports other interrupt modes, the driver only
supports high-level interrupts at the moment, because other modes could
not be tested so far.

Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210406120921.2484986-7-j.neuschaefer@gmx.net