drm/msm: #define MAX_<OBJECT> in msm_drv.h

dpu uses these elsewhere in the driver (in addition to increasing
MAX_PLANES, that'll come later), so pull them out into #define.

Changes in v3:
- None

Signed-off-by: Jeykumar Sankaran <jsanka@codeaurora.org>
[seanpaul pulled this out of the dpu megapatch]
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>