msm: kgsl: Clean up adreno_spin_idle_debug

Make the debug function target specific since
it was anyways used in only two places and it also
simplifies a bunch of indirect register reads
we had to do because of ADRENO_REG enum.

Change-Id: I20fcd91339639d999d475dae60f95a357721b71d
Signed-off-by: Urvashi Agrawal <urvaagra@codeaurora.org>