REALTEK_RTL8195AM: Expose SystemCoreClock via cmsis.h

This change is necessary as updated CMSIS/RTX require the
SystemCoreClock symbol.

Author: bulislaw

targets/TARGET_Realtek/TARGET_AMEBA/TARGET_RTL8195A/device/rtl8195a.h

@@ -32,7 +32,7 @@
 #include "hal_efuse.h"
 #include "hal_soc_ps_monitor.h"
 #include "diag.h"
-
+#include "system_8195a.h"
 
 // from RDC team
 #ifdef CONFIG_MBED_ENABLED