habanalabs: helper function to validate export params

Validate export parameters in a dedicated function instead of in the
main export flow.
This will be useful later when support to export dmabuf for devices
with virtual memory will be added.

Signed-off-by: Ohad Sharabi <osharabi@habana.ai>
Reviewed-by: Oded Gabbay <ogabbay@kernel.org>
Signed-off-by: Oded Gabbay <ogabbay@kernel.org>