serial: move CFG_NS9750_UART to CONFIG_NS9750_UART

move also conditional compilation to Makefile

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
diff --git a/include/configs/ns9750dev.h b/include/configs/ns9750dev.h
index f30cb46..746a56e 100644
--- a/include/configs/ns9750dev.h
+++ b/include/configs/ns9750dev.h
@@ -56,7 +56,7 @@
 /*
  * Hardware drivers
  */
-#define CFG_NS9750_UART			1	/* use on-chip UART */
+#define CONFIG_NS9750_UART		1	/* use on-chip UART */
 #define CONFIG_DRIVER_NS9750_ETHERNET	1	/* use on-chip ethernet */
 
 /*