sysctl: Move jiffies converters to kernel/time/jiffies.c

sysctl: Move jiffies converters to kernel/time/jiffies.c

Move integer jiffies converters (proc_dointvec{_,_ms_,_userhz_}jiffies
and proc_dointvec_ms_jiffies_minmax) to kernel/time/jiffies.c. Error
stubs for when CONFIG_PRCO_SYSCTL is not defined are not reproduced
because all the jiffies converters go through proc_dointvec_conv which
is already stubbed. This is part of the greater effort to move sysctl
logic out of kernel/sysctl.c thereby reducing merge conflicts in
kernel/sysctl.c.

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