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/taurus_defconfig b/configs/taurus_defconfig
index d9a2d61..16a804b 100644
--- a/configs/taurus_defconfig
+++ b/configs/taurus_defconfig
@@ -66,6 +66,7 @@
 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