tty: serial: sh-sci: Hide earlycon config question

Renesas H8/300 and ARM platforms use DT and support earlycon, so most
users want earlycon support to be enabled.

On SuperH platforms, earlycon is not yet supported.

Hence follow the above rationale to configure the default, unless
CONFIG_EXPERT is enabled.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>