kbuild: Use Kbuild.include

This commit adjusts some files to use Kbuild.include.

 - Use cc-option defined in Kbuild.include
    (Delete cc-option in config.mk)
 - Use cc-version defined in
    (Delete cc-version in config.mk)
 - Move binutils-version and dtc-version to Kbuild.include
     by analogy to cc-version

This commit also adds srctree (same as SRCTREE)
to use Kbuild scripts.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
5 files changed