drm/msm/dsi: drop unused GPIOs handling

Neither disp-enable-gpios nor disp-te-gpios are defined in the schema.
None of the board DT files use those GPIO pins. Drop them from the
driver.

Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Marijn Suijten <marijn.suijten@somainline.org>
Patchwork: https://patchwork.freedesktop.org/patch/598734/
Link: https://lore.kernel.org/r/20240613-dpu-handle-te-signal-v2-3-67a0116b5366@linaro.org