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/api/api_storage.c b/api/api_storage.c
index 8bed2f3..6fc6f44 100644
--- a/api/api_storage.c
+++ b/api/api_storage.c
@@ -63,7 +63,7 @@
 	specs[ENUM_MMC].type = DEV_TYP_STOR | DT_STOR_MMC;
 	specs[ENUM_MMC].name = "mmc";
 #endif
-#if defined(CONFIG_CMD_SATA)
+#if defined(CONFIG_SATA)
 	specs[ENUM_SATA].max_dev = CONFIG_SYS_SATA_MAX_DEVICE;
 	specs[ENUM_SATA].enum_started = 0;
 	specs[ENUM_SATA].enum_ended = 0;