dt-bindings: kbuild: Pass DT_SCHEMA_FILES to dt-validate

In preparation for supporting validation of DTB files, the full
processed schema will always be needed in order to extract type
information from it. Therefore, the processed schema containing only
what DT_SCHEMA_FILES specifies won't work. Instead, dt-validate has
gained an option, -l or --limit, to specify which schema(s) to use for
validation.

As the command line option is new, we the minimum dtschema version must be
updated.

Cc: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220310160513.1708182-2-robh@kernel.org