rtos/FreeRTOS: solve some conflicting usage of thread id. (#865)

* rtos/FreeRTOS: solve some conflicting usage of thread id.

1.
There are some RISCV-specific usage of thread_id, which has conflict with upstream.
Some adaptions are made in this patch, to make sure OpenOCD is sending a clear thread list to gdb.

2.
Use freertos_read_struct_value for xSchedulerRunning.

Change-Id: I001a88a0c6d8eac98a389c0217b4897f28124840
Signed-off-by: Chao Du <duchao@eswincomputing.com>

* fix typo.

Change-Id: Id6546cc74de44bbee7e44b7cb29b769a2f35ec4a

* correct the data type.

Change-Id: I28c7e111e569d94ba5f6e1ae21745ddb34d4dd12

* changes as per the review comment.

Change-Id: Ica4c705a8f2657700dc27e24790287ca802480fd

* another macro replacement.

Change-Id: Ia9330fed32d917cf87804051ba1b8d6ac42cfb7b

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Signed-off-by: Chao Du <duchao@eswincomputing.com>