xen/arm: mm: Clear boot pagetables before bringing-up each secondary CPU

xen/arm: mm: Clear boot pagetables before bringing-up each secondary CPU

At the moment, boot pagetables are only cleared once at boot. This means
when booting CPU2 (and onwards) then boot pagetables will not be
cleared.

To keep the interface exactly the same for all secondary CPU, the boot
pagetables are now cleared before bringing-up each secondary CPU.

Signed-off-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Volodymyr Babchuk <volodymyr_babchuk@epam.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
Release-acked-by: Juergen Gross <jgross@suse.com>