xen/arm32: mm: Avoid to zero and clean cache for CPU0 domheap

xen/arm32: mm: Avoid to zero and clean cache for CPU0 domheap

The page-table walker is configured to use the same shareability and
cacheability as the access performed when updating the page-tables. This
means cleaning the cache for CPU0 domheap is unnecessary.

Furthermore, CPU0 page-tables are part of Xen binary and will already be
zeroed before been used. So it is pointless to zero the domheap again.

Signed-off-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Andrii Anisov <andrii_anisov@epam.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>