x86/paravirt: Use PVOP_* for paravirt calls

Doing unconditional indirect calls through the pv_ops vector is weird.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Juergen Gross <jgross@suse.com>
Link: https://lore.kernel.org/r/20210624095148.437720419@infradead.org