[POWERPC] PS3: Update sys-manager button events

PS3 firmware 1.94 added the source of power and reset events to the
payload of the system manager POWER_PRESSED and RESET_PRESSED events.

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