Add clock generator node for CV1800B and CV1812H.

Until now, It uses DT override to minimize duplication. This may
change in the future. See the last link for the discussion on
maintaining DT of CV1800 series.

Link: https://github.com/milkv-duo/duo-files/blob/6f4e9b8ecb459e017cca1a8df248a19ca70837a3/duo/datasheet/CV1800B-CV1801B-Preliminary-Datasheet-full-en.pdf
Link: https://lore.kernel.org/all/IA1PR20MB495373158F3B690EF3BF2901BB8BA@IA1PR20MB4953.namprd20.prod.outlook.com/Reviewed-by: Chen Wang <unicorn_wang@outlook.com>
Link: https://lore.kernel.org/r/IA1PR20MB4953ED6A4B57773865F49D6DBB262@IA1PR20MB4953.namprd20.prod.outlook.comSigned-off-by: Inochi Amaoto <inochiama@outlook.com>
Signed-off-by: Chen Wang <unicorn_wang@outlook.com>