dom0/pvh: fix processing softirqs during memory map population

dom0/pvh: fix processing softirqs during memory map population

Make sure softirqs are processed after every successful call to
guest_physmap_add_page. Even if only a single page is to be added,
it's unknown whether the p2m or the IOMMU will require splitting the
provided page into smaller ones, and thus in case of having to break
a 1G page into 4K entries the amount of time taken by a single of
those additions will be non-trivial. Stay on the safe side and check
for pending softirqs on every successful loop iteration.

Fixes: 5427134eae ('x86: populate PVHv2 Dom0 physical memory map')
Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>