drm/msm/dp: Replace open-coded drm_dp_read_dpcd_caps()

This function duplicates the common function drm_dp_read_dpcd_caps().
The array of DPCD registers filled in is one size larger than the
function takes, but from what I can tell that extra byte was never used.
Resize the array and use the common function to reduce the code here.

Cc: Vinod Polimera <quic_vpolimer@quicinc.com>
Cc: Kuogee Hsieh <quic_khsieh@quicinc.com>
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Tested-by: Kuogee Hsieh <quic_khsieh@quicinc.com>
Reviewed-by: Kuogee Hsieh <quic_khsieh@quicinc.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/554981/
Link: https://lore.kernel.org/r/20230829184735.2841739-2-swboyd@chromium.org


Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>