sandbox: Fix up building for of-platdata

There is no devicetree with of-platdata. Update a few uclasses to allow
them to be built for sandbox_spl. Also drop the i2c-gpio from SPL to avoid
build errors, since it does not support of-platdata.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/rtc/rtc-uclass.c b/drivers/rtc/rtc-uclass.c
index 8035f7f..b406bab 100644
--- a/drivers/rtc/rtc-uclass.c
+++ b/drivers/rtc/rtc-uclass.c
@@ -174,5 +174,7 @@
 UCLASS_DRIVER(rtc) = {
 	.name		= "rtc",
 	.id		= UCLASS_RTC,
+#if !CONFIG_IS_ENABLED(OF_PLATDATA)
 	.post_bind	= dm_scan_fdt_dev,
+#endif
 };