x86, hpet: Introduce x86_msi_ops.setup_hpet_msi

This function pointer can be overwritten by the IRQ
remapping code. The irq_remapping_enabled check can be
removed from default_setup_hpet_msi.

Signed-off-by: Joerg Roedel <joro@8bytes.org>
Acked-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>