powerpc: Make generic_memcpy() private to copy_32.S

generic_memcpy() is only called from copy_32.S, so there's no reason for
it to be global.

Reported-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/lib/copy_32.S

@@ -217,7 +217,7 @@ _GLOBAL(memcpy)
 	bdnz	40b
 65:	blr
 
-_GLOBAL(generic_memcpy)
+generic_memcpy:
 	srwi.	r7,r5,3
 	addi	r6,r3,-4
 	addi	r4,r4,-4