M23: Fix compile error with mbed fault handler

M23 doesn't implement Main Extension. So like M0/M0+, these registers HFSR/
MMFSR/BFSR/UFSR/DFSR are not present on M23. Remove access to them in mbed
fault handler for M23 targets.

Author: ccli8

platform/TARGET_CORTEX_M/mbed_fault_handler.c

@@ -98,7 +98,7 @@ MBED_NOINLINE void print_context_info(void)
     //Capture CPUID to get core/cpu info
     mbed_error_printf("\nCPUID: %08" PRIX32, SCB->CPUID);
 
-#if !defined(TARGET_M0) && !defined(TARGET_M0P)
+#if !defined(TARGET_M0) && !defined(TARGET_M0P) && !defined(TARGET_M23)
     //Capture fault information registers to infer the cause of exception
     mbed_error_printf("\nHFSR : %08" PRIX32
                       "\nMMFSR: %08" PRIX32