[SPARC64]: Make kprobe implementation more robust.

Switch over to use the single-step scheme which x86 uses
which is to execute the kprobe instruction in the
kprobe->insn[] area.  Also, make sure the kprobe execution
runs fully with interrupts disabled, so we do not deadlock.

This required adding code to fix things up as a result of
the instruction executing at a PC which is different from
where it would normally execute.  For example, if the
instruction is a PC-relative branch, we have to adjust the
final PC value.
Signed-off-by: David S. Miller <davem@davemloft.net>