dt-bindings: display/msm: move DSI PHY bindings to phy/ subdir

dt-bindings: display/msm: move DSI PHY bindings to phy/ subdir

Historically DSI PHY bindings landed to the display/msm subdir, however
they describe PHYs and as such they should be in the phy/ subdir.
Follow the example of other Qualcomm display-related PHYs (HDMI, eDP)
and move bindings for the Qualcomm DSI PHYs to the correct subdir.

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@oss.qualcomm.com>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Acked-by: Vinod Koul <vkoul@kernel.org>
Patchwork: https://patchwork.freedesktop.org/patch/709008/
Link: https://lore.kernel.org/r/20260305-msm-dsi-phy-v1-1-0a99ac665995@oss.qualcomm.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>