asm-generic: adapt delay.h to common implementation

Several architectures are using a common delay.h implementation that
appears to have originated with the x86 architecture.  This common
implementation is a bit fuller than the current asm-generic version
and has some compile-time checks that should be interesting for all
architectures.

This patch takes the common delay.h version and replaces the rather
trivial asm-generic version with it.  As no architecture was actually
using asm-generic/delay.h, this change is rather innocuous; it will,
however, allow us to switch at least four architectures over to using
the asm-generic version.
Signed-off-by: Jonas Bonn <jonas@southpole.se>
Acked-by: Arnd Bergmann <arnd@arndb.de>

include/asm-generic/delay.h

 #ifndef __ASM_GENERIC_DELAY_H
 #define __ASM_GENERIC_DELAY_H
 
+/* Undefined functions to get compile-time errors */
+extern void __bad_udelay(void);
+extern void __bad_ndelay(void);
+
 extern void __udelay(unsigned long usecs);
+extern void __ndelay(unsigned long nsecs);
+extern void __const_udelay(unsigned long xloops);
 extern void __delay(unsigned long loops);
 
-#define udelay(n) __udelay(n)
+/* 0x10c7 is 2**32 / 1000000 (rounded up) */
+#define udelay(n) (__builtin_constant_p(n) ? \
+	((n) > 20000 ? __bad_udelay() : __const_udelay((n) * 0x10c7ul)) : \
+	__udelay(n))
+
+/* 0x5 is 2**32 / 1000000000 (rounded up) */
+#define ndelay(n) (__builtin_constant_p(n) ? \
+	((n) > 20000 ? __bad_ndelay() : __const_udelay((n) * 5ul)) : \
+	__ndelay(n))
 
 #endif /* __ASM_GENERIC_DELAY_H */