sandbox: i2c: Support i2c emulation with of-platdata

At present the i2c emulators require access to the devicetree, which is
not possible (by design) with of-platdata.

Add a way for drivers to record the of-platdata index of their emulator,
so that we can still find the emulator.

This allows i2c emulation to work with of-platdata.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/rtc/sandbox_rtc.c b/drivers/rtc/sandbox_rtc.c
index d0864b1..657e5c7 100644
--- a/drivers/rtc/sandbox_rtc.c
+++ b/drivers/rtc/sandbox_rtc.c
@@ -79,6 +79,18 @@
 };
 #endif
 
+static int sandbox_rtc_bind(struct udevice *dev)
+{
+#if CONFIG_IS_ENABLED(PLATDATA)
+	struct sandbox_i2c_rtc_plat_data *plat = dev_get_plat(dev);
+
+	/* Set up the emul_idx for i2c_emul_find() */
+	i2c_emul_set_idx(dev, plat->dtplat.sandbox_emul->idx);
+#endif
+
+	return 0;
+}
+
 static const struct rtc_ops sandbox_rtc_ops = {
 	.get = sandbox_rtc_get,
 	.set = sandbox_rtc_set,
@@ -97,5 +109,6 @@
 	.id	= UCLASS_RTC,
 	.of_match = sandbox_rtc_ids,
 	.ops	= &sandbox_rtc_ops,
+	.bind	= sandbox_rtc_bind,
 	ACPI_OPS_PTR(&sandbox_rtc_acpi_ops)
 };