sysctl: Move tainted ctl_table into kernel/panic.c

sysctl: Move tainted ctl_table into kernel/panic.c

Move the ctl_table with the "tainted" proc_name into kernel/panic.c.
With it moves the proc_tainted helper function.

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.

Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Reviewed-by: Kees Cook <kees@kernel.org>
Signed-off-by: Joel Granados <joel.granados@kernel.org>