[adm5120] do no longer rename amba-pl010 serial devices names

[adm5120] do no longer rename amba-pl010 serial devices names

Back in the days when we could not override /etc/inittab, it made a lot
of sense to rename ttyAM to ttyS since this was the only supported
serial device(s), we can now just put in an appropriate /etc/inittab file
now.

Signed-off-by: Florian Fainelli <florian@openwrt.org>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@34469 3c298f89-4303-0410-b956-a3cf2f4a3e73