qdutils : Retain the system property for default idle time.

Single idle time value is not working well on all targets as
power saving is dependent on specific GPU behavior on the device.
We need to come up with per target default idle time based on power
profiling. Retain the property to set default idle time per target.

Change-Id: I7ab4030f3e0078f96b504e5634cb7d96aeea60d5
1 file changed