arc770/axs101: fix console output

arc770/axs101: fix console output

While bumping kernel version kernel command line was
unintentionally modified in attempt to make it closer
to upstream version.

In case of AXS that has not only serial port but HDMI/USB
both capable of being debug console we have 2 entries in
kernel's command line:
------------------->8-----------------
console=tty0 console=ttyS3,115200n8
------------------->8-----------------

But as it turned out OpenWRT uses procd as init instead of
Busybox. And in its turn procd gets the first "console"
entry from kernel command line (/proc/cmdline) and uses it
if default inittab is used:
------------------->8-----------------
...
::askconsole:/bin/ash --login
------------------->8-----------------

So what we got is non-functional serial console.
That change removes "console=tty0" which brings serial
console back to life.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Felix Fietkau <nbd@openwrt.org>
Cc: Jo-Philipp Wich <jow@openwrt.org>
Cc: Jonas Gorski <jogo@openwrt.org>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@48325 3c298f89-4303-0410-b956-a3cf2f4a3e73