tools/dombuilder: xc_dom_x86 cleanup

tools/dombuilder: xc_dom_x86 cleanup

The two xc_dom_params structures for PV pagetables are never modified and can
live in .rodata.  Reduce their scope to the alloc_pgtable_*() functions which
construct xc_dom_image_x86 appropriately.

Rename {alloc,setup}_pgtables() to {alloc,setup}_pgtables_pv() to highlight
that they are PV only, and drop some _x86() suffixes from static helpers.

No functional change.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Wei Liu <wl@xen.org>