add xmc4000 to ci build

.github/workflows/build_arm.yml

@@ -57,6 +57,7 @@ jobs:
         - 'stm32f7'
         - 'stm32h7'
         - 'stm32l4'
+        - 'xmc4000'
     steps:
     - name: Setup Python
       uses: actions/setup-python@v2

hw/bsp/board_mcu.h

@@ -136,6 +136,10 @@
 
 #elif CFG_TUSB_MCU == OPT_MCU_MM32F327X
   #include "mm32_device.h"
+
+#elif CFG_TUSB_MCU == OPT_MCU_XMC4000
+  #include "xmc_device.h"
+
 #else
   #error "Missing MCU header"
 #endif