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/rainier_defconfig b/configs/rainier_defconfig
index aa3b9cc..0a0b4dd 100644
--- a/configs/rainier_defconfig
+++ b/configs/rainier_defconfig
@@ -1,6 +1,7 @@
 CONFIG_PPC=y
 CONFIG_4xx=y
 CONFIG_TARGET_SEQUOIA=y
+CONFIG_CMD_CHIP_CONFIG=y
 CONFIG_OF_BOARD_SETUP=y
 CONFIG_SYS_EXTRA_OPTIONS="RAINIER"
 CONFIG_BOOTDELAY=5