accel/habanalabs: use exported size from dma_buf and not from phys_pg_pack

The 'exported_size' member in 'struct hl_vm_phys_pg_pack' is used to
keep the exported dma-buf size, to be later used when the buffer is
mapped.
However it is possible that the same phys_pg_pack will be exported more
than once, and independently of when the mapping takes place.
Remove this member from the phys_pg_pack structure, and simply use the
size in the dma-buf object as the exported size when mapping.

Signed-off-by: Tomer Tayar <ttayar@habana.ai>
Reviewed-by: Oded Gabbay <ogabbay@kernel.org>
Signed-off-by: Oded Gabbay <ogabbay@kernel.org>