ANDROID: iommu/pkvm-iommu: Fix locking in maple tree usage

There are some problems with the maple tree usage at the moment:
- pviommu_domain_find() uses mas_find() which must be locked.
- pviommu_domain_remove_map() had a similar problem, but also it explicitly
  calls find and erase/insert non-atomically, so convert all of those to the
  unlocked version and use the tree lock on them.
- All allocations from unmap must be atomic

Bug: 357781595
Bug: 348382247
Signed-off-by: Mostafa Saleh <smostafa@google.com>
Reported-by: Aashish Sharma <shraash@google.com>
Change-Id: Ida8cfcfe3dc34ba7574d06eb1970602ab160173c