[SPARC64]: Fix several kprobes bugs.

- relbranch_fixup(), for non-branches, would end up setting
  regs->tnpc incorrectly, in fact it would set it equal to
  regs->tpc which would cause that instruction to execute twice

  Also, if this is not a PC-relative branch, we should just
  leave regs->tnpc as-is.  This covers cases like 'jmpl' which
  branch to absolute values.

- To be absolutely %100 safe, we need to flush the instruction
  cache for all assignments to kprobe->ainsn.insn[], including
  cases like add_aggr_kprobe()

- prev_kprobe's status field needs to be 'unsigned long' to match
  the type of the value it is saving

- jprobes were totally broken:
  = jprobe_return() can run in the stack frame of the jprobe handler,
    or in an even deeper stack frame, thus we'll be in the wrong
    register window than the one from the original probe state.

    So unwind using 'restore' instructions, if necessary, right
    before we do the jprobe_return() breakpoint trap.

  = There is no reason to save/res...