[POWERPC] ps3: always make sure were running on a PS3

Add missing checks to PS3 specific drivers ps3av and sys-manager to verify that
we are actually running on a PS3 (pointed out by Arnd).

Correct existing checks in other subsystems/drivers to return -ENODEV instead
of zero.

Signed-off-by: Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>

arch/powerpc/platforms/ps3/mm.c

@@ -294,7 +294,7 @@ static int __init ps3_mm_add_memory(void)
 	unsigned long nr_pages;
 
 	if (!firmware_has_feature(FW_FEATURE_PS3_LV1))
-		return 0;
+		return -ENODEV;
 
 	BUG_ON(!mem_init_done);