[BSP] Port to NuMicro M051 Series support for Nuvoton corp and fix compile warning

it tested and works fine on Nu-Tiny-SDK, and LED(P36) is blink.
it can compile in gcc, mdk5, and not support iar.
you also use scons --target=mdk5 command, to rebuild the mdk5 project.

1. adapt to M052xDN/xDE, M054xDN/xDE, M058xDN/xDE, M0516/xDN/xDE.
2. support heap memory management.
3. fix variable "c" was declared but never referenced,  when RT_USING_CONSOLE is disable.