rename symbol: CONFIG_ORION5X -> CONFIG_ARCH_ORION5X

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

Signed-off-by: Trevor Woerner <twoerner@gmail.com>
diff --git a/arch/arm/Makefile b/arch/arm/Makefile
index 5d32dec..2b44ffb 100644
--- a/arch/arm/Makefile
+++ b/arch/arm/Makefile
@@ -67,8 +67,7 @@
 machine-$(CONFIG_ARCH_MESON)		+= meson
 machine-$(CONFIG_ARCH_MVEBU)		+= mvebu
 machine-$(CONFIG_ARCH_OMAP2PLUS)	+= omap2
-# TODO: rename CONFIG_ORION5X -> CONFIG_ARCH_ORION5X
-machine-$(CONFIG_ORION5X)		+= orion5x
+machine-$(CONFIG_ARCH_ORION5X)		+= orion5x
 machine-$(CONFIG_ARCH_OWL)		+= owl
 machine-$(CONFIG_ARCH_RMOBILE)		+= rmobile
 machine-$(CONFIG_ARCH_ROCKCHIP)		+= rockchip