soc: arm: silabs: remove custom fixed MPU region definition

We remove the custom fixed MPU region definition from Silicon
Labs exx32 SoC definitions, as the common fixed MPU region
definition is now used.

Signed-off-by: Ioannis Glaropoulos <[email protected]>

Author: ioannisg

soc/arm/silabs_exx32/common/CMakeLists.txt

@@ -3,5 +3,3 @@
 zephyr_sources(soc.c soc_gpio.c)
 
 zephyr_sources_ifdef(CONFIG_SYS_POWER_MANAGEMENT soc_power.c)
-
-zephyr_sources_ifdef(CONFIG_ARM_MPU arm_mpu_regions.c)