During hard-reset, contexts are closed as part of the tear-down process.
After a context is closed, the driver cleans up the page tables of that
context in the device's DRAM. This action is both dangerous and
unnecessary.

It is unnecessary, because the device is going through a hard-reset, which
means the device's DRAM contents are no longer valid and the device's MMU
is being reset.

It is dangerous, because if the hard-reset came as a result of a PCI
freeze, this action may cause the entire host machine to hang.

Therefore, prevent all device PTE updates when a hard-reset operation is
pending.
Signed-off-by: NOded Gabbay <oded.gabbay@gmail.com>