MIPS: Add support for restartable sequences

MIPS: Add support for restartable sequences

Implement support for restartable sequences on MIPS, which requires 3
simple things:

  - Call rseq_handle_notify_resume() on return to userspace if
    TIF_NOTIFY_RESUME is set.

  - Call rseq_signal_deliver() to fixup the pre-signal stack frame when
    a signal is delivered whilst executing a restartable sequence
    critical section.

  - Select CONFIG_HAVE_RSEQ.

Signed-off-by: Paul Burton <[email protected]>
Reviewed-by: James Hogan <[email protected]>
Patchwork: https://patchwork.linux-mips.org/patch/19523/
Cc: Ralf Baechle <[email protected]>
Cc: Mathieu Desnoyers <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Paul E. McKenney <[email protected]>
Cc: Boqun Feng <[email protected]>
Cc: [email protected]
Cc: [email protected]