rename symbol: CONFIG_STM32 -> CONFIG_ARCH_STM32

Have this symbol follow the pattern of all other such symbols.

Signed-off-by: Trevor Woerner <twoerner@gmail.com>
diff --git a/arch/arm/Makefile b/arch/arm/Makefile
index e91b37f..94eb50b 100644
--- a/arch/arm/Makefile
+++ b/arch/arm/Makefile
@@ -73,7 +73,7 @@
 machine-$(CONFIG_ARCH_S5PC1XX)		+= s5pc1xx
 machine-$(CONFIG_ARCH_SNAPDRAGON)	+= snapdragon
 machine-$(CONFIG_ARCH_SOCFPGA)		+= socfpga
-machine-$(CONFIG_STM32)			+= stm32
+machine-$(CONFIG_ARCH_STM32)		+= stm32
 machine-$(CONFIG_ARCH_STM32MP)		+= stm32mp
 machine-$(CONFIG_ARCH_SUNXI)		+= sunxi
 machine-$(CONFIG_ARCH_TEGRA)		+= tegra