dt-bindings: clock: convert lpc1850-cgu.txt to yaml format

Convert lpc1850-cgu.txt to yaml format.

Additional changes:
- remove extra clock source nodes in example.
- remove clock consumer in example.
- remove clock-output-names and clock-clock-indices from required list to
  match existed dts.

Signed-off-by: Frank Li <Frank.Li@nxp.com>
Link: https://lore.kernel.org/r/20250606162410.1361169-1-Frank.Li@nxp.com


Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>