msm: kgsl: Increase IDLE_TIMEOUT for 2D core to 20secs

Increasing the hang detection time for 2D core from
10 secs to 20 secs to avoid False GPU Hangs.
Some c2d test cases are taking more than 10 secs
to process which results in a False GPU Hang.

Change-Id: Ice5e4b719adb44cd13fb8164bafedce1049416f7
CRs-Fixed: 454439
Signed-off-by: Vikram Orre <vorre@codeaurora.org>