ENGR00236879 Enhance VPU driver to handle API call sequence abnormal abort

ENGR00236879 Enhance VPU driver to handle API call sequence abnormal abort

Some application may exit without calling neccessay API to wrap up VPU
after it receives error message.

This could lead to system hang because driver will power off VPU
(vpu_release) while VPU may still be busy.

We require application to strictly follow the API call sequence even in
error handling case. Meanwhile, we enhance VPU driver to protect against
such abnormal abort, to prevent system hang at least.

If the last instance is closed, VPU will gate off or power off only if
VPU is idle.

Signed-off-by: Hongzhang Yang <Hongzhang.Yang@freescale.com>