irqchip: Add Sunplus SP7021 interrupt controller driver

Add interrupt controller driver for Sunplus SP7021 SoC.

This is the interrupt controller in P-chip which collects all interrupt
sources in P-chip and routes them to parent interrupt controller in C-chip.

Signed-off-by: Qin Jian <qinjian@cqplus1.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>