i2c: Update drivers to use enum for speed

Convert the obvious uses of i2c bus speeds to use the enum.

Use livetree access for code changes.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Heiko Schocher <hs@denx.de>
diff --git a/drivers/i2c/mvtwsi.c b/drivers/i2c/mvtwsi.c
index 0a2dafc..382cf4b 100644
--- a/drivers/i2c/mvtwsi.c
+++ b/drivers/i2c/mvtwsi.c
@@ -805,8 +805,9 @@
 				    "cell-index", -1);
 	dev->slaveadd = fdtdec_get_int(gd->fdt_blob, dev_of_offset(bus),
 				       "u-boot,i2c-slave-addr", 0x0);
-	dev->speed = fdtdec_get_int(gd->fdt_blob, dev_of_offset(bus),
-				    "clock-frequency", 100000);
+	dev->speed = dev_read_u32_default(bus, "clock-frequency",
+					  I2C_SPEED_STANDARD_RATE);
+
 	return 0;
 }