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/cmd/Kconfig b/cmd/Kconfig
index 90d9337..c80ac36 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -736,6 +736,7 @@
 
 config CMD_SATA
 	bool "sata - Access SATA subsystem"
+	select SATA
 	help
 	  SATA (Serial Advanced Technology Attachment) is a serial bus
 	  standard for connecting to hard drives and other storage devices.