Convert CONFIG_CMD_PCA953X to Kconfig

This converts the following to Kconfig:
   CONFIG_CMD_PCA953X

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
diff --git a/configs/xpedite550x_defconfig b/configs/xpedite550x_defconfig
index af56226..98e7124 100644
--- a/configs/xpedite550x_defconfig
+++ b/configs/xpedite550x_defconfig
@@ -21,6 +21,7 @@
 # CONFIG_CMD_HASH is not set
 CONFIG_CMD_JFFS2=y
 # CONFIG_CMD_IRQ is not set
+CONFIG_CMD_PCA953X=y
 # CONFIG_MMC is not set
 CONFIG_MTD_NOR_FLASH=y
 CONFIG_PHYLIB=y