dt-bindings: display/msm: dp-controller: fix fallback for SM6350

dt-bindings: display/msm: dp-controller: fix fallback for SM6350

Currently SM6350 uses qcom,sm8350-dp as a fallback compatible entry.
This works, but adding DP MST support will reveal that this SoC is
not fully compatible with SM8350 platform: the former one doesn't
provide MST support, while the latter one will get it. DT schema for
SM8350 is going to demand MST-related clocks which SM6350 doesn't
provide.

Add new entry for SM6350 with fallback to SC7180 (which belongs to the
same generation and also doesn't have MST support). SC7180 has been
supported by the Linux kernel long ago (and long before SM8350 support
was added).

Fixes: 39086151593a ("dt-bindings: display: msm: dp-controller: document SM6350 compatible")
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Patchwork: https://patchwork.freedesktop.org/patch/672571/
Link: https://lore.kernel.org/r/20250903-dp_mst_bindings-v8-2-7526f0311eaa@oss.qualcomm.com