xen/arm: mm: Initialize page-tables earlier

xen/arm: mm: Initialize page-tables earlier

Since commit f60658c6ae "xen/arm: Stop relocating Xen", the function
setup_page_tables() does not require any information from the FDT.

So the initialization of the page-tables can be done much earlier in the
boot process. The earliest setup_page_tables() can be called is after
traps have been initialized, so we can get backtrace if an error
occurred.

Moving the initialization of the page-tables also avoid the dance to map
the FDT again in the new set of page-tables.

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