x86: fix do_update_va_mapping_otherdomain() wrt translated domains

x86: fix do_update_va_mapping_otherdomain() wrt translated domains

While I can't seem to find any users of this hypercall (being a likely
explanation of why the problem wasn't noticed so far), just like for
do_mmu_update() paged-out and shared page handling is needed here. Move
all this logic into mod_l1_entry(), which then also results in no
longer
- doing any of this handling for non-present PTEs,
- acquiring two temporary page references when one is already more than
  enough.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Release-acked-by: Julien Grall <julien.grall@linaro.org>