Convert CONFIG_CMD_CHIP_CONFIG to Kconfig

This converts the following to Kconfig:
   CONFIG_CMD_CHIP_CONFIG

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/icon_defconfig b/configs/icon_defconfig
index c2e510d..117fcb5 100644
--- a/configs/icon_defconfig
+++ b/configs/icon_defconfig
@@ -2,6 +2,7 @@
 CONFIG_VIDEO=y
 CONFIG_4xx=y
 CONFIG_TARGET_ICON=y
+CONFIG_CMD_CHIP_CONFIG=y
 CONFIG_OF_BOARD_SETUP=y
 CONFIG_BOOTDELAY=5
 # CONFIG_CONSOLE_MUX is not set