word-at-a-time.h: fix some Kbuild files

arch/tile added word-at-a-time.h after the patch that added generic-y
entries; the generic-y entry is now stale.

arch/h8300 is newer than the generic-y patch for word-at-a-time.h,
and needs a generic-y entry.

arch/powerpc seems to have gotten a generic-y entry by mistake in
the first patch; this change removes it.

Signed-off-by: Chris Metcalf <[e-mail]>

arch/h8300/include/asm/Kbuild

···
 generic-y += ucontext.h
 generic-y += unaligned.h
 generic-y += vga.h
+generic-y += word-at-a-time.h
 generic-y += xor.h

arch/powerpc/include/asm/Kbuild

···
 generic-y += preempt.h
 generic-y += rwsem.h
 generic-y += vtime.h
-generic-y += word-at-a-time.h

arch/tile/include/asm/Kbuild

···
 generic-y += termios.h
 generic-y += trace_clock.h
 generic-y += types.h
-generic-y += word-at-a-time.h
 generic-y += xor.h