ARM: am3517_evm: Enable TCA6416PW GPIO Expander

With DM_I2C and DM_GPIO working, this patch can enable the
GPIO expander on the I2C bus.  This GPIO expander is connected
to some of the DIP switches and can now read the status of these
pins.
Signed-off-by: NAdam Ford <aford173@gmail.com>

configs/am3517_evm_defconfig

@@ -38,6 +38,7 @@ CONFIG_DEFAULT_DEVICE_TREE="am3517-evm"
 CONFIG_SPL_OF_PLATDATA=y
 # CONFIG_ENV_IS_IN_FAT is not set
 CONFIG_ENV_IS_IN_NAND=y
+CONFIG_DM_PCA953X=y
 CONFIG_MMC_OMAP_HS=y
 CONFIG_NAND=y
 CONFIG_SYS_NAND_BUSWIDTH_16BIT=y