Convert CONFIG_CMD_BAT to Kconfig

This converts the following to Kconfig:
   CONFIG_CMD_BAT

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/board/ti/sdp4430/Kconfig b/board/ti/sdp4430/Kconfig
index 5826d8f..36f1852 100644
--- a/board/ti/sdp4430/Kconfig
+++ b/board/ti/sdp4430/Kconfig
@@ -9,4 +9,7 @@
 config SYS_CONFIG_NAME
 	default "omap4_sdp4430"
 
+config CMD_BAT
+	bool "Enable board-specific battery command"
+
 endif