m68k: Implement ndelay() based on the existing udelay() logic

#define udelay(n) (__builtin_constant_p(n) ? \

	((n) > 20000 ? __bad_udelay() : __const_udelay(n)) : __udelay(n))

/*

 * nanosecond delay:

 *

 * ((((HZSCALE) >> 11) * (loops_per_jiffy >> 11)) >> 6) is the number of loops

 * per microsecond

 *

 * 1000 / ((((HZSCALE) >> 11) * (loops_per_jiffy >> 11)) >> 6) is the number of

 * nanoseconds per loop

 *

 * So n / ( 1000 / ((((HZSCALE) >> 11) * (loops_per_jiffy >> 11)) >> 6) ) would

 * be the number of loops for n nanoseconds

 */

/*

 * The simpler m68k and ColdFire processors do not have a 32*32->64

 * multiply instruction. So we need to handle them a little differently.

 * We use a bit of shifting and a single 32*32->32 multiply to get close.

 * This is a macro so that the const version can factor out the first

 * multiply and shift.

 */

#define	HZSCALE		(268435456 / (1000000 / HZ))

#define ndelay(n) __delay(DIV_ROUND_UP((n) * ((((HZSCALE) >> 11) * (loops_per_jiffy >> 11)) >> 6), 1000));

#endif /* defined(_M68K_DELAY_H) */