softmmu/physmem: Remove the ifdef __linux__ around the pagesize functions

Now that host_memory_backend_pagesize() is not depending on the hugetlb
memory path handling anymore, we can also remove the #ifdef and the
TOCTTOU comment from the calling functions - the code should now work
equally well on all host architectures.

Message-Id: <20220810125720.3849835-3-thuth@redhat.com>
Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>