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: Jeffrey Hugo <jeffrey.l.hugo@gmail.com>
Signed-off-by: Rob Clark <robdclark@chromium.org>