mapper: update documentation on locking

Update the locking documentation to require all 1D buffers
"lock in place". Previously, the framework was able to get 1D
buffers that locked in place via ion. The ion interface is no
longer directly accessible. Some framework use cases still need
1D buffers that lock in place so add the requirement to mapper.

Bug: 120493579
Test: N/A
Change-Id: Ib903efdbeeb8c44ed70c3c6022d6792d05df1a63