arm64: Change elfcore for_each_mte_vma() to use VMA iterator

Rework for_each_mte_vma() to use a VMA iterator instead of an explicit
linked-list. This will allow easy integration with the maple tree work
which removes the VMA list altogether.

Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20220218023650.672072-1-Liam.Howlett@oracle.com
[will: Folded in fix from Catalin]
Link: https://lore.kernel.org/r/YhUcywqIhmHvX6dG@arm.com
Signed-off--by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will@kernel.org>