arch/tile: implement arch_ptrace using user_regset on tile

This patch changes arch_ptrace on tile so that it uses user_regset
to implement the PTRACE_GETREGS and PTRACE_SETREGS operations.

Signed-off-by: Simon Marchi <simon.marchi@polymtl.ca>
Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>