asm-generic: add generic versions of common headers

These are all kernel internal interfaces that get copied
around a lot. In most cases, architectures can provide
their own optimized versions, but these generic versions
can work as well.

I have tried to use the most common contents of each
header to allow existing architectures to migrate easily.

Thanks to Remis for suggesting a number of cleanups.

Signed-off-by: Remis Lima Baima <remis.developer@googlemail.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

include/asm-generic/irq.h

@@ -0,0 +1,18 @@
+#ifndef __ASM_GENERIC_IRQ_H
+#define __ASM_GENERIC_IRQ_H
+
+/*
+ * NR_IRQS is the upper bound of how many interrupts can be handled
+ * in the platform. It is used to size the static irq_map array,
+ * so don't make it too big.
+ */
+#ifndef NR_IRQS
+#define NR_IRQS 64
+#endif
+
+static inline int irq_canonicalize(int irq)
+{
+	return irq;
+}
+
+#endif /* __ASM_GENERIC_IRQ_H */