drm/msm/adreno: a5xx_power: Don't apply A540 lm_setup to other GPUs

While passing the A530-specific lm_setup func to A530 and A540
to !A530 was fine back when only these two were supported, it
certainly is not a good idea to send A540 specifics to smaller
GPUs like A508 and friends.

Signed-off-by: Konrad Dybcio <konrad.dybcio@somainline.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>