drm/msm/adreno: fix CP cycles stat retrieval on a7xx

a7xx_submit() should use the a7xx variant of the RBBM_PERFCTR_CP register
for retrieving the CP cycles value before and after the submitted command
stream execution.

Signed-off-by: Zan Dobersek <zdobersek@igalia.com>
Fixes: af66706a

 ("drm/msm/a6xx: Add skeleton A7xx support")
Patchwork: https://patchwork.freedesktop.org/patch/588445/
Signed-off-by: Rob Clark <robdclark@chromium.org>