pm: Fix device resume order

Devices need to be resumed in the reverse order they are suspended.
e.g: devA +---> devB ---> devD
          |
          +---> devC

They are initialized in the following order, devA -> devB -> devC ->
devD, and suspended starting from the end of the list, devD -> devC ->
devB -> devA. When they are suspended they are temporary put in a list
that is used later to resume them.

This list has to be iterated from the end to the beginning, otherwise a
device may be resumed before its parent.

Signed-off-by: Flavio Ceolin <flavio.ceolin@intel.com>