serial: 8250_ingenic: drop #if conditional surrounding earlycon code

The #if defined(CONFIG_SERIAL_EARLYCON) && !defined(MODULE)
conditional has been added to the OF_EARLYCON_DECLARE() define.

The same conditional can be dropped from 8250_ingenic.c because
the unused symbols will be marked as __maybe_unsed.
Also, the Kconfig dependency can become much simpler.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>