dt-bindings: copy process-schema-examples.yaml to process-schema.yaml

dt-bindings: copy process-schema-examples.yaml to process-schema.yaml

There are two processed schema files:

 - processed-schema-examples.yaml

    Used for 'make dt_binding_check'. This is always a full schema.

 - processed-schema.yaml

    Used for 'make dtbs_check'. This may be a full schema, or a smaller
    subset if DT_SCHEMA_FILES is given by a user.

If DT_SCHEMA_FILES is not specified, they are the same. You can copy
the former to the latter instead of running dt-mk-schema twice. This
saves the cpu time a lot when you do 'make dt_binding_check dtbs_check'
because building the full schema takes a couple of seconds.

If DT_SCHEMA_FILES is specified, processed-schema.yaml is generated
based on the specified yaml files.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Link: https://lore.kernel.org/r/20200625170434.635114-4-masahiroy@kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>