x86: Add sysctl flag CTLFLAG_TUN to loader tunables
The following sysctl variables are actually loader tunables. Add sysctl
flag CTLFLAG_TUN to them so that sysctl -T will report them correctly.
- machdep.idle
- machdep.idle_apl31
No functional change intended.
Reviewed by: kib, imp
MFC after: 3 days
Differential Revision: https://reviews.freebsd.org/D42113