rename symbol: CONFIG_KIRKWOOD -> CONFIG_ARCH_KIRKWOOD

Have this symbol follow the pattern of all other such symbols.
This patch also removes a TODO from the code.

Reviewed-by: Chris Packham <judge.packham@gmail.com>
Signed-off-by: Trevor Woerner <twoerner@gmail.com>
diff --git a/drivers/net/mvgbe.c b/drivers/net/mvgbe.c
index b0b8d34..6d56360 100644
--- a/drivers/net/mvgbe.c
+++ b/drivers/net/mvgbe.c
@@ -24,7 +24,7 @@
 #include <asm/byteorder.h>
 #include <asm/arch/cpu.h>
 
-#if defined(CONFIG_KIRKWOOD)
+#if defined(CONFIG_ARCH_KIRKWOOD)
 #include <asm/arch/soc.h>
 #elif defined(CONFIG_ARCH_ORION5X)
 #include <asm/arch/orion5x.h>