CMake rtos: add M55 to irq handlers, use m33 handlers = the same

Author: 0xc0170

cmsis/CMSIS_5/CMSIS/RTOS2/RTX/CMakeLists.txt

@@ -15,6 +15,8 @@ function(_mbed_get_cortex_m_exception_handlers toolchain_dir)
             set(STARTUP_RTX_FILE TARGET_M3/irq_cm3.S)
         elseif(${key} STREQUAL M33)
             set(STARTUP_RTX_FILE TARGET_M33/irq_armv8mml.S)
+        elseif(${key} STREQUAL M55)
+            set(STARTUP_RTX_FILE TARGET_M33/irq_armv8mml.S)
         elseif(${key} STREQUAL RTOS_M4_M7)
             set(STARTUP_RTX_FILE TARGET_RTOS_M4_M7/irq_cm4f.S)
         endif()