drm/msm/disp/dpu1/dpu_encoder: Remove a bunch of unused variables

Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c: In function ‘dpu_encoder_virt_mode_set’:
 drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c:981:31: warning: variable ‘num_dspp’ set but not used [-Wunused-but-set-variable]
 drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c:976:30: warning: variable ‘topology’ set but not used [-Wunused-but-set-variable]
 drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c: In function ‘_dpu_encoder_virt_enable_helper’:
 drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c:1099:26: warning: variable ‘priv’ set but not used [-Wunused-but-set-variable]
 drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c: In function ‘dpu_encoder_virt_disable’:
 drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c:1210:18: warning: variable ‘dpu_kms’ set but not used [-Wunused-but-set-variable]

Cc: Rob Clark <robdclark@gmail.com>
Cc: Sean Paul <sean@poorly.run>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: linux-arm-msm@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Cc: freedreno@lists.freedesktop.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Reviewed-by: Abhinav Kumar <abhinavk@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@chromium.org>