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/arch/arm/Makefile b/arch/arm/Makefile
index 2b44ffb..9b3ca97 100644
--- a/arch/arm/Makefile
+++ b/arch/arm/Makefile
@@ -60,8 +60,7 @@
 machine-$(CONFIG_ARCH_HIGHBANK)		+= highbank
 machine-$(CONFIG_ARCH_K3)		+= k3
 machine-$(CONFIG_ARCH_KEYSTONE)		+= keystone
-# TODO: rename CONFIG_KIRKWOOD -> CONFIG_ARCH_KIRKWOOD
-machine-$(CONFIG_KIRKWOOD)		+= kirkwood
+machine-$(CONFIG_ARCH_KIRKWOOD)		+= kirkwood
 machine-$(CONFIG_ARCH_LPC32XX)		+= lpc32xx
 machine-$(CONFIG_ARCH_MEDIATEK)		+= mediatek
 machine-$(CONFIG_ARCH_MESON)		+= meson