iris/bufmgr: round up vma reservations on DG2
For DG2 we can't share PDEs with different sized PTEs. To ensure 4K PTE buffers don't try to share a PDE with 64K PTE buffers we reserve VA up to the next alignment.
See https://patchwork.freedesktop.org/series/98996 for further details
Signed-off-by: Robert Beckett bob.beckett@collabora.com