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/smartweb_defconfig b/configs/smartweb_defconfig
index 8f9a19f..4545c70 100644
--- a/configs/smartweb_defconfig
+++ b/configs/smartweb_defconfig
@@ -49,6 +49,7 @@
 CONFIG_CLK=y
 CONFIG_CLK_AT91=y
 CONFIG_DFU_NAND=y
+CONFIG_AT91_GPIO=y
 # CONFIG_MMC is not set
 CONFIG_MTD=y
 CONFIG_MTD_RAW_NAND=y