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/Kconfig b/arch/arm/Kconfig
index 5864646..8bdcf34 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -553,7 +553,7 @@
 	help
 	  Support for TI's DaVinci platform.
 
-config KIRKWOOD
+config ARCH_KIRKWOOD
 	bool "Marvell Kirkwood"
 	select ARCH_MISC_INIT
 	select BOARD_EARLY_INIT_F