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/Kconfig b/arch/arm/Kconfig
index 6152b11..ef7da27 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1607,7 +1607,7 @@
 	  Support for UniPhier SoC family developed by Socionext Inc.
 	  (formerly, System LSI Business Division of Panasonic Corporation)
 
-config STM32
+config ARCH_STM32
 	bool "Support STMicroelectronics STM32 MCU with cortex M"
 	select CPU_V7M
 	select DM