dt-bindings: msm/dsi: Add 10nm phy for msm8998 compatible

The DSI phy on MSM8998 is a 10nm design like SDM845, however it has some
slightly different quirks which need to be handled by drivers.  Provide
a separate compatible to assist in handling the specifics.
Signed-off-by: NJeffrey Hugo <jeffrey.l.hugo@gmail.com>
Signed-off-by: NRob Clark <robdclark@chromium.org>

Documentation/devicetree/bindings/display/msm/dsi.txt

@@ -88,6 +88,7 @@ Required properties:
   * "qcom,dsi-phy-28nm-8960"
   * "qcom,dsi-phy-14nm"
   * "qcom,dsi-phy-10nm"
+  * "qcom,dsi-phy-10nm-8998"
 - reg: Physical base address and length of the registers of PLL, PHY. Some
   revisions require the PHY regulator base address, whereas others require the
   PHY lane base address. See below for each PHY revision.