kconfig: add CONFIG_LOCALVERSION and CONFIG_LOCALVERSION_AUTO

Copy Kconfig options from "init/Kconfig" of Linux v3.16 tag
and adjust some parts of the help document.

Move CONFIG_SPL, CONFIG_TPL, ... etc. to "Boot images" menu.

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