tty: Remove to support serial for S5P6442

According to removing ARCH_S5P6442, we don't need to support
serial for S5P6442.

Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>