drm/msm/dpu: drop (mostly) unused DPU_NAME_SIZE define

drm/msm/dpu: drop (mostly) unused DPU_NAME_SIZE define

This define is used only in one place, in dpu_encoder debugfs code.
Inline the value and drop the define completely.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Marijn Suijten <marijn.suijten@somainline.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/538303/
Link: https://lore.kernel.org/r/20230521192230.9747-2-dmitry.baryshkov@linaro.org
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>