Current img hash claims sys and periph gate clocks
and this can be gated in system suspend scenarios.

Add support for Device pm ops for img hash to gate
the clocks claimed by img hash.
Signed-off-by: Govindraj Raja <Govindraj.Raja@imgtec.com>
Reviewed-by: Will Thomas <will.thomas@imgtec.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>