x86: Add an i8042 device for boards that have it

Some boards have an i8042 device. Enable the driver for all x86 boards, and
add a device tree node for those which may have this keyboard.

Also adjust the configuration so that i8042 is always separate from the VGA,
and rename the stdin driver accordingly. With this commit the keyboard will
not work, but it is fixed in the next commit.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>