dt-bindings: phy: Convert mixel,mipi-dsi-phy to json-schema

This patch converts the mixel,mipi-dsi-phy binding to
DT schema format using json-schema.

Comparing to the plain text version, the new binding adds
the 'assigned-clocks', 'assigned-clock-parents' and
'assigned-clock-rates' properites, otherwise 'make dtbs_check'
would complain that there are mis-matches.  Also, the new
binding requires the 'power-domains' property since all potential
SoCs that embed this PHY would provide a power domain for it.
The example of the new binding takes reference to the latest
dphy node in imx8mq.dtsi.

Cc: Guido Günther <agx@sigxcpu.org>
Cc: Kishon Vijay Abraham I <kishon@ti.com>
Cc: Vinod Koul <vkoul@kernel.org>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: NXP Linux Team <linux-imx@nxp.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Guido Günther <agx@sigxcpu.org>
Signed-off-by: Liu Ying <victor.liu@nxp.com>
Link: https://lore.kernel.org/r/20220419010852.452169-4-victor.liu@nxp.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>