The calculation to get TI_CPU based off of SPRG3 was just plain wrong,
meaning that we were getting garbage for the CPU number on 6xx/G3/G4
based SMP boxes in this code.

Just offset off the stack pointer (to get to thread_info) like all the
other references to TI_CPU do.

This was pointed out by Chen Gong <G.Chen@freescale.com>

[paulus@samba.org - use rlwinm r12,r11,... instead of
 rlwinm r12,r1,...; tophys()]
Signed-off-by: NKumar Gala <galak@kernel.crashing.org>
Acked-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: NPaul Mackerras <paulus@samba.org>