Replace explicit TUNABLE_INT to sysctl with CTLFLAG_TUN

• Replace tunables-only hw.psm.synaptics_support, hw.psm.trackpoint_support, and hw.psm.elantech_support with respective sysctls declared with CTLFLAG_TUN. It simplifies checking them in userland, also makes them easier to get discovered by user
• Get rid of debug.psm.loglevel and hw.psm.tap_enabled TUNABLE_INT declaration by adding CTLFLAG_TUN to read/write sysctls that were already declared for these tunables.

Suggested by: jhb