The previous implementation will always blocks the reader/writer.
However, at least FinSh would expect the device to be nonblocking ---
read should return 0 when there is no data in it.

Add the APIs that will discard the old data when rb is full.

RT_RINGBUFFER_SIZE could mean "the size of the whole buffer", "the size
of the empty space" or "the size of the data". Moreover, it's never a
micro anymore. Change it to rt_ringbuffer_data_len before it's too late.
Also, RT_RINGBUFFER_EMPTY is changed to rt_ringbuffer_space_len.

device/pipe: add rt_pipe_{init,detach}

This provide the possibility that allocate the buffer of the ringbuffer
on a specific region, instead of always mallocing it. It also bring us
the benefit of using pipe device on the systems without heap.

fix debug output of scheduler

When print the thread names, we should use "%.*s" instead of bare "%s".

SEP6200 Support

K60 fxxxx

simulator: update to support simulator for linux

At91sam9260

memheap: don't alloc/memcpy when there is next node is enough for realloc

When realloc a bigger space and the next node is free and big enough, we
should directly relocate the next node instead of doing alloc/memcpy.
The new method not only faster in this cases, it would avoid memory
fragment as well.