xen/x86: Remove PVH support

xen/x86: Remove PVH support

We are replacing existing PVH guests with new implementation.

We are keeping xen_pvh_domain() macro (for now set to zero) because
when we introduce new PVH implementation later in this series we will
reuse current PVH-specific code (xen_pvh_gnttab_setup()), and that
code is conditioned by 'if (xen_pvh_domain())'. (We will also need
a noop xen_pvh_domain() for !CONFIG_XEN_PVH).

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
OraBug: 26662731

(cherry picked from commit 063334f30543597430f172bd7690d21e3590e148)
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Reviewed-by: Joao Martins <joao.m.martins@oracle.com>
Conflicts:
       arch/x86/xen/enlighten.c
       (We don't have xen_dom0_set_legacy_features() and xen_cpuhp_setup())
       arch/x86/xen/smp.h
       (xen_smp_intr_*() are not in our header files)
       arch/x86/xen/xen-head.S
       (difference in a comment)
       include/xen/xen.h
       (xen_have_vector_callback is not in upstream's definition of xen_pvh_domain())