drm/msm/dpu: Add support for AR30 format

Commit da7716a2 ("drm/msm/dpu: Add support for XR30 format") enabled
support for the 10-bit XR30 color format but missed enabling support for the
corresponding per-pixel alpha-blending AR30 color format.

Declaring only XR30 but not AR30 color format support can trigger bugs in
userspace. KDE KWin compositor versions prior to 5.27.3 for example prefer
10-bit color formats, rendering a 1cm^2 black box around the cursor due to
missing per-pixel alpha-blending.

Signed-off-by: Leonard Lausen <leonard@lausen.nl>
Reviewed-by: Jessica Zhang <quic_jesszhan@quicinc.com>
Tested-by: Jessica Zhang <quic_jesszhan@quicinc.com> # Trogdor (sc7180)
Patchwork: https://patchwork.freedesktop.org/patch/527985/
Link: https://lore.kernel.org/r/6f33219dc848ccd7122bce6933338033aa18c33c@lausen.nl


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