powerpc: Fix delay functions for 601 processors

My earlier merge of delay.h introduced a timebase-based udelay for
32-bit machines but also broke the 601, which doesn't have the
timebase register.  This fixes it by using the 601's RTC register on
the 601, and also moves __delay() and udelay() to be out-of-line in
arch/powerpc/kernel/time.c.  These functions aren't really performance
critical, after all.

Signed-off-by: Paul Mackerras <paulus@samba.org>

arch/powerpc/kernel/misc_32.S

@@ -27,14 +27,6 @@
 
 	.text
 
-	.align	5
-_GLOBAL(__delay)
-	cmpwi	0,r3,0
-	mtctr	r3
-	beqlr
-1:	bdnz	1b
-	blr
-
 /*
  * This returns the high 64 bits of the product of two 64-bit numbers.
  */