Kconfig: Add CONFIG_SATA to enable SATA

At present CONFIG_CMD_SATA enables the 'sata' command which also brings
in SATA support. Some boards may wish to enable SATA without the command.
Add a separate CONFIG to permit this.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/board/bachmann/ot1200/ot1200.c b/board/bachmann/ot1200/ot1200.c
index c0a8b64..74f652e 100644
--- a/board/bachmann/ot1200/ot1200.c
+++ b/board/bachmann/ot1200/ot1200.c
@@ -338,7 +338,7 @@
 
 	leds_on();
 
-#ifdef CONFIG_CMD_SATA
+#ifdef CONFIG_SATA
 	setup_sata();
 #endif