x86/shadow: dirty VRAM tracking is needed for HVM only

x86/shadow: dirty VRAM tracking is needed for HVM only

Move shadow_track_dirty_vram() into hvm.c (requiring two static
functions to become non-static). More importantly though make sure we
don't de-reference d->arch.hvm.dirty_vram for a non-HVM guest. This was
a latent issue only just because the field lives far enough into struct
hvm_domain to be outside the part overlapping with struct pv_domain.

While moving shadow_track_dirty_vram() some purely typographic
adjustments are being made, like inserting missing blanks or putting
breaces on their own lines.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Tim Deegan <tim@xen.org>