video: tegra: host: gk20a: fix PDE update sequence

video: tegra: host: gk20a: fix PDE update sequence

Current sequence :
- delete page tables memory
- update PDE entry and mark above page tables invalid

With this sequence, it is possible to have valid PDE entries
with already freed page table and this could lead us to
invalid memory accesses.

Fix this by switching the sequence as follows :
- update PDE entry and mark page tables invalid
- delete page tables memory

Bug 1577947

Change-Id: Icc3a8c74bbf1bf59e41e0322cfc279d15690aa9d
Signed-off-by: Deepak Nibade <dnibade@nvidia.com>
Reviewed-on: http://git-master/r/670323
(cherry-picked from commit 56f738b4c4ee188ec1f69b91615cd9728ff18cf0)
Reviewed-on: http://git-master/r/671196
Tested-by: Terje Bergstrom <tbergstrom@nvidia.com>
Reviewed-by: Terje Bergstrom <tbergstrom@nvidia.com>
GVS: Gerrit_Virtual_Submit