scripts: Move Kconfig contents to cmd/Kconfig

On case-insensitive file systems we have collision between
scripts/kconfig/ directory and scripts/Kconfig file. This patch moves
scripts/Kcofnig contents to cmd/Kconfig to fix that.

Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
Acked-by: Masahiro Yamada <yamada.masahiro@socionext.com>