arch/tile: clean up tile-specific PTRACE_SETOPTIONS

Use the newer idioms for setting PTRACE_O_xxx and PT_TRACE_xxx flags.
Only set/clear tile-specific flags if the generic routine returns
success, since otherwise we want to avoid setting any flags at all.
Atomically update the ptrace flags with the new values.  Eliminate
the PT_TRACE_MASK_TILE bitmask and just shift PTRACE_O_MASK_TILE.
Add a BUILD_BUG_ON to avoid overlapping with generic bits.

Acked-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>