kconfig: sync kconfig files with Linux 3.18-rc1

This commit imports Kconfig updates from Linux 3.18-rc1.

'kvmconfig' and 'tinyconfig' help message have been commented out
since they are unavailable at least now;  in the future perhaps
we can implement 'tinyconfig' to disable most of CONFIG_CMD_* to
create a very small U-Boot image.

[1] commit 3aaefce10351 by Josh Triplett
x86, platform, kconfig: move kvmconfig functionality to a helper

[2] commit 0da1d4a0b951 by Josh Triplett
x86: Add "make tinyconfig" to configure the tiniest possible kernel

[3] commit c40724d3f381 by Brian Norris
  kconfig: lxdialog: fix spelling

[4] commit 7285996aa000 by Brian Norris
  kconfig: nconfig: fix multi-byte UTF handling

Signed-off-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>