x86/dom0: use MEMF_no_scrub during Dom0 construction

x86/dom0: use MEMF_no_scrub during Dom0 construction

Now that idle scrub is the default option, all memory is marked as dirty
and alloc_domheap_pages() will do eager scrubbing by default. This can
lead to longer Dom0 construction and potentially to a watchdog timeout,
especially on older H/W (e.g. Harpertown).

Pass MEMF_no_scrub to optimise this process since there is little point
in scrubbing memory for Dom0.

Signed-off-by: Sergey Dyasli <sergey.dyasli@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>