Convert CONFIG_CMD_SATA to Kconfig

This converts the following to Kconfig:
   CONFIG_CMD_SATA

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/configs/nitrogen6q2g_defconfig b/configs/nitrogen6q2g_defconfig
index a19d093..baa509d 100644
--- a/configs/nitrogen6q2g_defconfig
+++ b/configs/nitrogen6q2g_defconfig
@@ -19,6 +19,7 @@
 CONFIG_CMD_USB=y
 CONFIG_CMD_USB_MASS_STORAGE=y
 CONFIG_CMD_GPIO=y
+CONFIG_CMD_SATA=y
 CONFIG_CMD_DHCP=y
 CONFIG_CMD_MII=y
 CONFIG_CMD_PING=y