habanalabs: don't do memory scrubbing when unmapping

There is no need to do memory scrub when unmapping anymore as it is
an overhead as long as we have a single user at any given time.

Remove that code and change return value of free_phys_pg_pack to void

Signed-off-by: Dafna Hirschfeld <dhirschfeld@habana.ai>
Reviewed-by: Oded Gabbay <ogabbay@kernel.org>
Signed-off-by: Oded Gabbay <ogabbay@kernel.org>