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/configs/km_kirkwood_128m16_defconfig b/configs/km_kirkwood_128m16_defconfig
index d185100..9bbbfd9 100644
--- a/configs/km_kirkwood_128m16_defconfig
+++ b/configs/km_kirkwood_128m16_defconfig
@@ -1,7 +1,7 @@
 CONFIG_ARM=y
 CONFIG_SYS_DCACHE_OFF=y
 CONFIG_ARCH_CPU_INIT=y
-CONFIG_KIRKWOOD=y
+CONFIG_ARCH_KIRKWOOD=y
 CONFIG_SYS_TEXT_BASE=0x07d00000
 CONFIG_TARGET_KM_KIRKWOOD=y
 CONFIG_ENV_SIZE=0x2000