powerpc/ps3: Add missing check for PS3 to rtc-ps3 platform device registration

On non-PS3, we get:

| kernel BUG at drivers/rtc/rtc-ps3.c:36!

because the rtc-ps3 platform device is registered unconditionally in a kernel
with builtin support for PS3.
Reported-by: Sachin Sant <sachinp@in.ibm.com>
Signed-off-by: Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
Acked-by: Geoff Levand <geoffrey.levand@am.sony.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/platforms/ps3/time.c

@@ -21,6 +21,7 @@
 #include <linux/kernel.h>
 #include <linux/platform_device.h>
 
+#include <asm/firmware.h>
 #include <asm/rtc.h>
 #include <asm/lv1call.h>
 #include <asm/ps3.h>
@@ -84,6 +85,9 @@ static int __init ps3_rtc_init(void)
 {
 	struct platform_device *pdev;
 
+	if (!firmware_has_feature(FW_FEATURE_PS3_LV1))
+		return -ENODEV;
+
 	pdev = platform_device_register_simple("rtc-ps3", -1, NULL, 0);
 	if (IS_ERR(pdev))
 		return PTR_ERR(pdev);