gpio: Add Aspeed GPIO driver

The Aspeed GPIO driver supports the GPIO controllers found in the
AST2400, AST2500 and AST2600 BMC SoCs. The implementation is a cut-down
copy of the upstream Linux kernel driver, adapted for u-boot.

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
index 1c963c2..be64303 100644
--- a/drivers/gpio/Kconfig
+++ b/drivers/gpio/Kconfig
@@ -127,6 +127,13 @@
 	  may be dedicated as a general purpose I/O or be assigned to
 	  a function of an embedded peripheral.
 
+config ASPEED_GPIO
+	bool "Aspeed GPIO Driver"
+	help
+	  Say yes here to support the Aspeed GPIO driver. The controller
+	  is found in the AST2400, AST2500 and AST2600 BMC SoCs and
+	  provides access to over 200 GPIOs on each chip.
+
 config DA8XX_GPIO
 	bool "DA8xx GPIO Driver"
 	help