Revert "msm: kgsl: Use IDLE interrupt to switch to NAP state"

This reverts commit 688272a0.

The HW is very strict in its definition of the word "busy". Even
register reads and writes are "busy" enough to make the GPU send
an idle interrupt when the register access is finished.  This ends
up in lots of extra interrupts in key places like initialization
and hang detection defeating the purpose of faster idle detection.

Change-Id: Ic0dedbad39dbbddd08c5a8eca7a34d4c214bd8b4
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>