Convert CONFIG_AT91_GPIO to Kconfig

This converts the following to Kconfig:
   CONFIG_AT91_GPIO

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/vinco_defconfig b/configs/vinco_defconfig
index 2684324..8ca7556 100644
--- a/configs/vinco_defconfig
+++ b/configs/vinco_defconfig
@@ -31,6 +31,7 @@
 CONFIG_DEFAULT_DEVICE_TREE="at91-vinco"
 CONFIG_ENV_IS_IN_SPI_FLASH=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
+CONFIG_AT91_GPIO=y
 CONFIG_SUPPORT_EMMC_BOOT=y
 CONFIG_SPI_FLASH=y
 CONFIG_SF_DEFAULT_MODE=0