Add the definition for GR-LYCHEE in mbed_rtx.h

In mbed_rtx.h file, I added the definition for GR-LYCHEE to use the "Dynamic Heap" processing when the target is GR_LYCHEE.

Author: TomoYamanaka

targets/TARGET_RENESAS/mbed_rtx.h

@@ -18,6 +18,7 @@
 
 #include <stdint.h>
 
+#if defined(TARGET_RZ_A1H) || defined(TARGET_GR_LYCHEE)
 #define OS_IDLE_THREAD_STACK_SIZE   512
 
 #if defined(__CC_ARM)
@@ -43,5 +44,6 @@
 #else
     #error "no toolchain defined"
 #endif
+#endif
 
 #endif  // MBED_MBED_RTX_H