signal: Move signal ctl tables into signal.c

signal: Move signal ctl tables into signal.c

Move print-fatal-signals into its own const ctl table array in
kernel/signal.c. This is part of a greater effort to move ctl tables
into their respective subsystems which will reduce the merge conflicts
in kernel/sysctl.c.

Signed-off-by: Joel Granados <joel.granados@kernel.org>