soc: arm: st_stm32f2x: Convert Kconfig input prompt to uppercase

The STM32F2x was the only one of the STM32 series with a lowercase
input prompt.  This looks odd in the SoC selection in 'menuconfig'.

Signed-off-by: Detlev Zundel <[email protected]>

Author: laodzu

soc/arm/st_stm32/stm32f2/Kconfig.series

@@ -4,7 +4,7 @@
 # SPDX-License-Identifier: Apache-2.0
 
 config SOC_SERIES_STM32F2X
-	bool "stm32f2x Series MCU"
+	bool "STM32F2x Series MCU"
 	select ARM
 	select CPU_CORTEX_M3
 	select CPU_CORTEX_M_HAS_DWT