Implement kernel stack tracing hooks for sparc64

[Jakub Jermář]

Implement kernel hooks for stack tracing on sparc64.

Currently, there are the following open problems:

• userspace windows are flushed to the userspace window buffer, so the uspace tracing hooks should somehow find the respective window save areas there
• istate_t does not save fp (but it is located in the memory stack near the istate structure)
• consider ticket #10 (Register window thrashing)
• wait for integration of ticket #142 (sun4v support)