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/gateworks/gw_ventana/gw_ventana.c b/board/gateworks/gw_ventana/gw_ventana.c
index 6b950ee..40ee1b6 100644
--- a/board/gateworks/gw_ventana/gw_ventana.c
+++ b/board/gateworks/gw_ventana/gw_ventana.c
@@ -633,7 +633,7 @@
 #endif
 	setup_ventana_i2c();
 
-#ifdef CONFIG_CMD_SATA
+#ifdef CONFIG_SATA
 	setup_sata();
 #endif
 	/* read Gateworks EEPROM into global struct (used later) */