Revert "arm64: Change elfcore for_each_mte_vma() to use VMA iterator"

This reverts commit 3a4f7ef4.

Revert this temporary bodge. It only existed to ease integration with
the maple tree work for the 5.18 merge window and that doesn't appear
to have landed in any case.

Signed-off-by: Will Deacon <will@kernel.org>