ARC: Enable fatal signals on boot for dev platforms

It's very convenient to have fatal signals enabled on developemnt
platform as this allows to catch problems that happen early in
user-space (like crashing init or dynamic loader).

Otherwise we may either enable it later from alive taregt console
by "echo 1 > /proc/sys/kernel/print-fatal-signals" but:
 1. We might be unfortunate enough to not reach working console
 2. Forget to enable fatal signals and miss something interesting

Given we're talking about development platforms here it shouldn't
be a problem if a bit more data gets printed to debug console.

Moreover this makes behavior of all our dev platforms predictable
as today some platforms already have it enabled and some don't -
which is way too inconvenient.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>