asm/head: fix power save wakeup register corruption
asm/head: fix power save wakeup register corruption

Power save wakeup handlers can clobber r30 before testing for state
loss and avoiding restoring non-volatile GPRs. Fix this by using r5
instead (and move the register usage to one place, for clarity).

Cc: 74fabe089ecbd0f3f71683991d9e2780a4de1f4a@lists.ozlabs.org
Fixes: 8a43bf86b7 ("core/exceptions: implement an exception handler for non-powersave sresets")
Signed-off-by: Nicholas Piggin <24829078df5003d9dd1dd871ca2aeb0b1cf95ef4@gmail.com>
Signed-off-by: Oliver O'Halloran <3dfaff8fa6ae977f042064a112a6aac576279b9b@gmail.com>

legoater/skiboot,open-power/skiboot,qemu/skiboot,open-power/skiboot,qemu/skiboot,shenki/skiboot,shenki/skiboot,qemu/skiboot,qemu/skiboot,open-power/skiboot,legoater/skiboot,legoater/skiboot,legoater/skiboot,qemu/skiboot,legoater/skiboot,shenki/skiboot,shenki/skiboot,open-power/skiboot,open-power/skiboot,shenki/skiboot