habanalabs: use smallest possible alignment for virtual addresses

Change the acquiring of a device virtual address for mapping by using the
smallest possible alignment, rather than the biggest, depending on the
page size used by the user for allocating the memory. This will lower the
virtual space memory consumption.

Signed-off-by: Omer Shpigelman <oshpigelman@habana.ai>
Reviewed-by: Oded Gabbay <oded.gabbay@gmail.com>
Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>