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/arch/arm/imx-common/Makefile b/arch/arm/imx-common/Makefile
index b7cb434..fc69172 100644
--- a/arch/arm/imx-common/Makefile
+++ b/arch/arm/imx-common/Makefile
@@ -25,7 +25,7 @@
 endif
 ifeq ($(SOC),$(filter $(SOC),mx6 mx7))
 obj-y 	+= cache.o init.o
-obj-$(CONFIG_CMD_SATA) += sata.o
+obj-$(CONFIG_SATA) += sata.o
 obj-$(CONFIG_IMX_VIDEO_SKIP) += video.o
 obj-$(CONFIG_IMX_RDC) += rdc-sema.o
 obj-$(CONFIG_IMX_BOOTAUX) += imx_bootaux.o