Cleanup uart1-related node on ELECOM WAB-I1750-PS and enable it for
"SERIAL" port on the case.
"SERIAL" port can be used for OpenWrt console by adding the following
line to /etc/inittab and rebooting:
ttyATH1::askfirst:/usr/libexec/login.sh
Signed-off-by: INAGAKI Hiroshi <musashino.open@gmail.com>