Add GDB thread command support

This commit updates the MRI core to version 1.1.20200413.0 which now
includes support for GDB thread commands. It also provides the required
implementations of the Platform_Rtos*() functions for ThreadDebug and
KernelDebug to enable that new thread support in each of those debug
monitors.

Changes to the MRI core include:
* Improve T packet response - Added support for notifying GDB of
  current thread id, if running in a RTOS environment, and expanding on
  the cause of debug trap stops to let GDB know which watchpoint, if
  any, was the cause.
* vCont support - This commit adds support for single stepping,
  continuing, and ranged single stepping in single and multi threaded
  environments. The ranged single stepping is a really cool feature that
  reduces the round trip traffic that usually occurs between MRI and GDB
  when single stepping through code at source code level. Ranged single
  stepping will just continue execution on each single stepped
  instruction that corresponds to the current source code line and only
  send a T stop response to GDB when the program counter points to an
  instruction not in the range of the current source code line.
* Implement qf/sThreadInfo request to list threads to GDB - Allows MRI
  to respond to GDB's qfThreadInfo & qsThreadInfo requests with a list
  of the RTOS thread IDs.
* Added qThreadExtraInfo support - Allows GDB to call and retrieve
  extra information about a particular thread ID as a string. For RTX,
  it currently returns the thread name and its state (running, waiting,
  etc.)
* Add support for Hg command - GDB sends this command to indicate which
  thread's registers should be reference by the next 'g' or 'G'
  command. Renamed the ScatterGather class to MriContext and now use it
  from the higher level MRI core code to access the CPU register
  contents. When Hg is sent, MRI will switch the RTX thead context used
  for future register read and write operations.
* Added support for the T command - The T command is sent by GDB to see
  if a particular thread ID is still active or not. GDB sends this
  command to a remote stub when the user types the "thread id#" command
  into the user interface to see if the specified ID is valid or not.

Author: adamgreen

Diff for: libraries/KernelDebug/src/KernelDebug.cpp

@@ -58,7 +58,8 @@
 
 #include <stdint.h>
 #include <core/token.h>
-#include <core/scatter_gather.h>
+#include <core/context.h>
+#include <core/platforms.h>
 
 
 /* Give friendly names to the indices of important registers in the context scatter gather list. */
@@ -91,7 +92,8 @@
 
 typedef struct
 {
-    ScatterGather       context;
+    MriContext          context;
+    PlatformTrapReason  reason;
     uint32_t            taskSP;
     uint32_t            sp;
     uint32_t            exceptionNumber;