dt/bindings: clk: Add YAML schemas for LS1028A Display Clock bindings

LS1028A has a clock domain PXLCLK0 used for provide pixel clocks to Display
output interface. Add a YAML schema for this.

Signed-off-by: Wen He <wen.he_1@nxp.com>
Signed-off-by: Michael Walle <michael@walle.cc>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lkml.kernel.org/r/20191213083402.35678-1-wen.he_1@nxp.com


Signed-off-by: Stephen Boyd <sboyd@kernel.org>