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/wb50n_defconfig b/configs/wb50n_defconfig
index 86a8549..e764c30 100644
--- a/configs/wb50n_defconfig
+++ b/configs/wb50n_defconfig
@@ -33,6 +33,7 @@
 CONFIG_SYS_REDUNDAND_ENVIRONMENT=y
 CONFIG_SYS_RELOC_GD_ENV_ADDR=y
 CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG=y
+CONFIG_AT91_GPIO=y
 CONFIG_MTD=y
 CONFIG_MTD_RAW_NAND=y
 # CONFIG_SYS_NAND_USE_FLASH_BBT is not set