Add threshold support methods
Add threshold support methods

Add type traits and methods in support of sensor thresholds.

Change-Id: I92a0c17aba4899c0d48bf76039d48a6ed1ee7f95
Signed-off-by: Brad Bishop <713d098c0be4c8fd2bf36a94cd08699466677ecd@fuzziesquirrel.com>

openbmc/phosphor-hwmon,openbmc/phosphor-hwmon