i2c: Rename CONFIG_SYS_I2C to CONFIG_SYS_I2C_LEGACY

It is quite confusing that CONFIG_SYS_I2C selects the legacy I2C and
CONFIG_DM_I2C selects the current I2C. The deadline to migrate I2C is less
than a year away.

Also we want to have a CONFIG_I2C for U-Boot proper just like we have
CONFIG_SPL_I2C for SPL, so we can simplify the Makefile rules.

Rename this symbol so it is clear it is going away.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Heiko Schocher <hs@denx.de>
diff --git a/include/configs/ls1046a_common.h b/include/configs/ls1046a_common.h
index 6d927b1..f49766b 100644
--- a/include/configs/ls1046a_common.h
+++ b/include/configs/ls1046a_common.h
@@ -134,7 +134,7 @@
 
 /* I2C */
 #if !CONFIG_IS_ENABLED(DM_I2C)
-#define CONFIG_SYS_I2C
+#define CONFIG_SYS_I2C_LEGACY
 #define CONFIG_SYS_I2C_MXC_I2C1		/* enable I2C bus 1 */
 #define CONFIG_SYS_I2C_MXC_I2C2		/* enable I2C bus 2 */
 #define CONFIG_SYS_I2C_MXC_I2C3		/* enable I2C bus 3 */