x86/paravirt: add spin_lock_flags lock op

It is useful for a pv_lock_ops backend to know whether interrupts are
enabled or not in the context a spin_lock is being called.  This
allows it to enable interrupts while spinning, which could be
particularly helpful when spinning becomes blocking.

The default implementation just calls the normal spin_lock op,
ignoring the flags.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>