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/at91rm9200ek_defconfig b/configs/at91rm9200ek_defconfig
index 0b02591..2aaf879 100644
--- a/configs/at91rm9200ek_defconfig
+++ b/configs/at91rm9200ek_defconfig
@@ -22,6 +22,7 @@
 CONFIG_CMD_FAT=y
 CONFIG_ENV_IS_IN_FLASH=y
 CONFIG_ENV_ADDR=0x10040000
+CONFIG_AT91_GPIO=y
 # CONFIG_MMC is not set
 CONFIG_MTD_NOR_FLASH=y
 CONFIG_FLASH_CFI_DRIVER=y