[POWERPC] PS3: Compare firmware version

Add a utility routine ps3_compare_firmware_version() to compare system
firmware versions.  Uses the existing ps3_get_firmware_version() routine.

Signed-off-by: Masakazu Mokuno <mokuno@sm.sony.co.jp>
Signed-off-by: Geoff Levand <geoffrey.levand@am.sony.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>