[POWERPC] PS3: Use system reboot on restart

The PS3 Other OS boot flag is not checked when an LPAR reboot is done,
so the ps3-boot-game-os utility fails to reboot the system into the
Game OS.  This fix changes the PS3 restart handler from requesting an
PS3_SM_NEXT_OP_LPAR_REBOOT to requesting an PS3_SM_NEXT_OP_SYS_REBOOT.

Signed-off-by: Geoff Levand <geoffrey.levand@am.sony.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>