powerpc: mm: add VM_IOREMAP flag to the vmalloc area

powerpc: mm: add VM_IOREMAP flag to the vmalloc area

Currently, for vmalloc areas with flag VM_IOREMAP set, except of the
specific alignment clamping in __get_vm_area_node(), they will be

 1) Shown as ioremap in /proc/vmallocinfo;

 2) Ignored by /proc/kcore reading via vread()

So for the io mapping in ioremap_phb() of ppc, we should set VM_IOREMAP in
flag to make it handled correctly as above.

Link: https://lkml.kernel.org/r/20230206084020.174506-7-bhe@redhat.com
Signed-off-by: Baoquan He <bhe@redhat.com>
Reviewed-by: Lorenzo Stoakes <lstoakes@gmail.com>
Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Cc: Dan Carpenter <error27@gmail.com>
Cc: Stephen Brennan <stephen.s.brennan@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>