irqchip: Add GICv2 specific ACPI boot support

ACPI kernel uses MADT table for proper GIC initialization. It needs to
parse GIC related subtables, collect CPU interface and distributor
addresses and call driver initialization function (which is hardware
abstraction agnostic). In a similar way, FDT initialize GICv1/2.

NOTE: This commit allow to initialize GICv1/2 basic functionality.
While now simple GICv2 init call is used, any further GIC features
require generic infrastructure for proper ACPI irqchip initialization.
That mechanism and stacked irqdomains to support GICv2 MSI/virtualization
extension, GICv3/4 and its ITS are considered as next steps.

CC: Jason Cooper <jason@lakedaemon.net>
CC: Marc Zyngier <marc.zyngier@arm.com>
CC: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@amd.com>
Tested-by: Yijing Wang <wangyijing@huawei.com>
Tested-by: Mark Langsdorf <mlangsdo@redhat.com>
Tested-by: Jon Masters <jcm@redhat.com>
Tested-by: Timur Tabi <timur@codeaurora.org>
Tested-by: Robert Richter <rrichter@cavium.com>
Acked-by: Robert Richter <rrichter@cavium.com>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Acked-by: Jason Cooper <jason@lakedaemon.net>
Reviewed-by: Grant Likely <grant.likely@linaro.org>
Signed-off-by: Tomasz Nowicki <tomasz.nowicki@linaro.org>
Signed-off-by: Hanjun Guo <hanjun.guo@linaro.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>

include/linux/acpi_irq.h

@@ -0,0 +1,10 @@
+#ifndef _LINUX_ACPI_IRQ_H
+#define _LINUX_ACPI_IRQ_H
+
+#include <linux/irq.h>
+
+#ifndef acpi_irq_init
+static inline void acpi_irq_init(void) { }
+#endif
+
+#endif /* _LINUX_ACPI_IRQ_H */