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/wandboard/wandboard.c b/board/wandboard/wandboard.c
index 2c9dc8b..438bc0e 100644
--- a/board/wandboard/wandboard.c
+++ b/board/wandboard/wandboard.c
@@ -379,7 +379,7 @@
 #if defined(CONFIG_VIDEO_IPUV3)
 	setup_display();
 #endif
-#ifdef CONFIG_CMD_SATA
+#ifdef CONFIG_SATA
 	/* Only mx6q wandboard has SATA */
 	if (is_cpu_type(MXC_CPU_MX6Q))
 		setup_sata();