Separating xe_vma- and page-table state

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

Hi,

It's IMO become apparent both in the system allocator discussion and in
the patch that enables the presence of invalid vmas that we need to be
better at separating xe_vma and page-table state, so that xe_vma state
would contain things that are mostly immutable and that the user
requested: PAT index, memory attributes, requested tile presence etc,
whereas the page-table state would contain mutable state like actual
tile presence, invalidaton state and MMU notifier. 

So far we have had no reason to separate the two, but with hmmptr we
would likely end up with multiple page-table regions per xe-vma, and
with the patch discussed earlier we could've easily reused
xe_vm_unbind_vma() that only touches the mutable page-table state and
does the correct locking.

The page table could would then typically take a const xe_vma *, and
and xe_pt_state *, or whatever we choose to call it. All xe_vmas except
hmmptr ones would have an 1:1 xe_vma <-> xe_pt_state relationship.

Thoughts, comments?

Thanks,
Thomas