gdbstub: Implement "Xfer:spaces" requests.
This is a part of Codebench IDE integration.

Signed-off-by: Alex Rozenman <Alex_Rozenman@mentor.com>
Initial support for platform registers visualization.
This is a part of Codebench integration.

Signed-off-by: Alex Rozenman <Alex_Rozenman@mentor.com>