powerpc/e500: make load_up_spe a normal fuction

So that we can call it when improving SPE switch like book3e did for fp
switch.

Signed-off-by: Liu Yu <yu.liu@freescale.com>
Signed-off-by: Olivia Yin <hong-hua.yin@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>